St Andrews Lynx

Well, first I'd make sure I was welcome back at my previous lab.  If they don't have a spot for you anymore, this whole thing is kind of pointless.  anyway, if they are willing to take you back, then I would say that you should approach the person you are working with now very diplomatically and explain that you feel that the subfield you are working on here isn't what you feel most fits your interests and further education.  Whatever you do, don't make it sound like it's the prof's fault.  He sounds like the type to go BOOM if he thinks you are pointing fingers at him in any way.  I don't know if i would mention where you are going to lab-wise as I'm not sure if this guy is jerk enough to bully the other lab's prof.  anyway, it's your education and your future.  You have the right to make decisions that go in the direction you want to go instead of the direction your profs try to push you.  Be strong but diplomatic.

NPR and high-quality newspapers/magazines (New Yorker, etc) are always a good reserve of small-talk fuel, especially in response to what people are telling you about themselves ("oh, you teach kindergarten? I heard on the radio the other day that they are implementing [interesting early education pilot program] in Colorado, do you think that would be a success?"). Asking people about the TV shows they are watching or recent films they've seen is another good way to find common ground. 
 
From talking to people from all walks of life, it actually seems like the teaching part of my grad school life is what others can relate to. They might not understand the intricacies of my chemistry sub-sub-field...but they can understand and empathise with my teaching responsibilities. They also don't need much prior pedagogical knowledge to understand classroom anecdotes.
 
The keys to interacting with folk from different social situations is (i) respectfulness (just because they dropped out of high school doesn't mean there is nothing you can learn from them (ii) a sense of humour (iii) interest in what they are saying. That way even if you don't say much during the gathering, they will still remember you as a respectful, interested person with a sense of humour.

Can we keep an interesting thread on topic and amicable?

I'm sorry to hear about your friend. I guess the person who sent the email was upset and didn't know how to break the news to you. Take care.

NPR and high-quality newspapers/magazines (New Yorker, etc) are always a good reserve of small-talk fuel, especially in response to what people are telling you about themselves ("oh, you teach kindergarten? I heard on the radio the other day that they are implementing [interesting early education pilot program] in Colorado, do you think that would be a success?"). Asking people about the TV shows they are watching or recent films they've seen is another good way to find common ground. 
 
From talking to people from all walks of life, it actually seems like the teaching part of my grad school life is what others can relate to. They might not understand the intricacies of my chemistry sub-sub-field...but they can understand and empathise with my teaching responsibilities. They also don't need much prior pedagogical knowledge to understand classroom anecdotes.
 
The keys to interacting with folk from different social situations is (i) respectfulness (just because they dropped out of high school doesn't mean there is nothing you can learn from them (ii) a sense of humour (iii) interest in what they are saying. That way even if you don't say much during the gathering, they will still remember you as a respectful, interested person with a sense of humour.

NPR and high-quality newspapers/magazines (New Yorker, etc) are always a good reserve of small-talk fuel, especially in response to what people are telling you about themselves ("oh, you teach kindergarten? I heard on the radio the other day that they are implementing [interesting early education pilot program] in Colorado, do you think that would be a success?"). Asking people about the TV shows they are watching or recent films they've seen is another good way to find common ground. 
 
From talking to people from all walks of life, it actually seems like the teaching part of my grad school life is what others can relate to. They might not understand the intricacies of my chemistry sub-sub-field...but they can understand and empathise with my teaching responsibilities. They also don't need much prior pedagogical knowledge to understand classroom anecdotes.
 
The keys to interacting with folk from different social situations is (i) respectfulness (just because they dropped out of high school doesn't mean there is nothing you can learn from them (ii) a sense of humour (iii) interest in what they are saying. That way even if you don't say much during the gathering, they will still remember you as a respectful, interested person with a sense of humour.

NPR and high-quality newspapers/magazines (New Yorker, etc) are always a good reserve of small-talk fuel, especially in response to what people are telling you about themselves ("oh, you teach kindergarten? I heard on the radio the other day that they are implementing [interesting early education pilot program] in Colorado, do you think that would be a success?"). Asking people about the TV shows they are watching or recent films they've seen is another good way to find common ground. 
 
From talking to people from all walks of life, it actually seems like the teaching part of my grad school life is what others can relate to. They might not understand the intricacies of my chemistry sub-sub-field...but they can understand and empathise with my teaching responsibilities. They also don't need much prior pedagogical knowledge to understand classroom anecdotes.
 
The keys to interacting with folk from different social situations is (i) respectfulness (just because they dropped out of high school doesn't mean there is nothing you can learn from them (ii) a sense of humour (iii) interest in what they are saying. That way even if you don't say much during the gathering, they will still remember you as a respectful, interested person with a sense of humour.

NPR and high-quality newspapers/magazines (New Yorker, etc) are always a good reserve of small-talk fuel, especially in response to what people are telling you about themselves ("oh, you teach kindergarten? I heard on the radio the other day that they are implementing [interesting early education pilot program] in Colorado, do you think that would be a success?"). Asking people about the TV shows they are watching or recent films they've seen is another good way to find common ground. 
 
From talking to people from all walks of life, it actually seems like the teaching part of my grad school life is what others can relate to. They might not understand the intricacies of my chemistry sub-sub-field...but they can understand and empathise with my teaching responsibilities. They also don't need much prior pedagogical knowledge to understand classroom anecdotes.
 
The keys to interacting with folk from different social situations is (i) respectfulness (just because they dropped out of high school doesn't mean there is nothing you can learn from them (ii) a sense of humour (iii) interest in what they are saying. That way even if you don't say much during the gathering, they will still remember you as a respectful, interested person with a sense of humour.

NPR and high-quality newspapers/magazines (New Yorker, etc) are always a good reserve of small-talk fuel, especially in response to what people are telling you about themselves ("oh, you teach kindergarten? I heard on the radio the other day that they are implementing [interesting early education pilot program] in Colorado, do you think that would be a success?"). Asking people about the TV shows they are watching or recent films they've seen is another good way to find common ground. 
 
From talking to people from all walks of life, it actually seems like the teaching part of my grad school life is what others can relate to. They might not understand the intricacies of my chemistry sub-sub-field...but they can understand and empathise with my teaching responsibilities. They also don't need much prior pedagogical knowledge to understand classroom anecdotes.
 
The keys to interacting with folk from different social situations is (i) respectfulness (just because they dropped out of high school doesn't mean there is nothing you can learn from them (ii) a sense of humour (iii) interest in what they are saying. That way even if you don't say much during the gathering, they will still remember you as a respectful, interested person with a sense of humour.

Write a long & detailed letter to your advisor telling him how he made you feel, cataloguing all your frustrations and all his failings...then burn the letter. 
 
Another (additional) option is to send them an email or write a nice card thanking them sincerely for their support and assistance in completing the program. Short, sweet, lying through your teeth if necessary. Give them a small gift (maybe a Starbucks gift card or something under $40 that they would appreciate). Sometimes killing 'em with kindness is the best way to get release, or maybe reaching out with a bit forgiveness will help your ex-advisor thaw and perhaps even volunteer an apology. It certainly won't do you any good to hold on to the bitterness and anger.

Write a long & detailed letter to your advisor telling him how he made you feel, cataloguing all your frustrations and all his failings...then burn the letter. 
 
Another (additional) option is to send them an email or write a nice card thanking them sincerely for their support and assistance in completing the program. Short, sweet, lying through your teeth if necessary. Give them a small gift (maybe a Starbucks gift card or something under $40 that they would appreciate). Sometimes killing 'em with kindness is the best way to get release, or maybe reaching out with a bit forgiveness will help your ex-advisor thaw and perhaps even volunteer an apology. It certainly won't do you any good to hold on to the bitterness and anger.

Write a long & detailed letter to your advisor telling him how he made you feel, cataloguing all your frustrations and all his failings...then burn the letter. 
 
Another (additional) option is to send them an email or write a nice card thanking them sincerely for their support and assistance in completing the program. Short, sweet, lying through your teeth if necessary. Give them a small gift (maybe a Starbucks gift card or something under $40 that they would appreciate). Sometimes killing 'em with kindness is the best way to get release, or maybe reaching out with a bit forgiveness will help your ex-advisor thaw and perhaps even volunteer an apology. It certainly won't do you any good to hold on to the bitterness and anger.

I think there is a difference between giving feedback after the final essay has been marked and before the student has turned in said draft (i.e, they want you to tell them how to make it into an A-grade essay rather than figuring it out by themselves). 

With any roommate from any country, the key to getting on well is communication.
If a roommate leaves their dirty dishes clogging up the sink for weeks of end...politely ask them to clean up and explain why the dishes are a problem. If a roommate has never lived independently and clearly has no idea how to clean a bathroom...go through the cleaning process with them. If a roommate makes a lot of noise at 3am...explain that you are trying to sleep at that time and their behaviour is inconsiderate. 
 
Be understanding to international visitors and always give them the benefit of the doubt. Some behaviour/actions might come off as unusual, but could in part be fuelled by homesickness, culture shock, differences in culture norms, etc. 
 
There are plenty of obnoxious, dirty, weird and loud American roommates out there in the world, too. Nationality of your roommate doesn't guarantee anything. 

I think that the main problem is that you're allowing yourself to get annoyed by it. I guess I would question why it is so specifically annoying (are you perhaps a little envious of the online attention they are getting from those posts? is there something else in your grad school life that is giving you stress, and you're offloading your annoyance/frustration onto something/body else?).
 
Instead of being annoyed, try to think positive thoughts about this person. They're working hard at their coursework, and they're getting good grades for it. Good for them. 

With any roommate from any country, the key to getting on well is communication.
If a roommate leaves their dirty dishes clogging up the sink for weeks of end...politely ask them to clean up and explain why the dishes are a problem. If a roommate has never lived independently and clearly has no idea how to clean a bathroom...go through the cleaning process with them. If a roommate makes a lot of noise at 3am...explain that you are trying to sleep at that time and their behaviour is inconsiderate. 
 
Be understanding to international visitors and always give them the benefit of the doubt. Some behaviour/actions might come off as unusual, but could in part be fuelled by homesickness, culture shock, differences in culture norms, etc. 
 
There are plenty of obnoxious, dirty, weird and loud American roommates out there in the world, too. Nationality of your roommate doesn't guarantee anything. 

I don't think switching advisors is the difference between a five year and a seven plus year PhD. It seems like it might be the difference between a PhD and no PhD. Not to stress you out, but don't fall victim to the sunk cost fallacy with your current, unsupportive advisor.

I think that the main problem is that you're allowing yourself to get annoyed by it. I guess I would question why it is so specifically annoying (are you perhaps a little envious of the online attention they are getting from those posts? is there something else in your grad school life that is giving you stress, and you're offloading your annoyance/frustration onto something/body else?).
 
Instead of being annoyed, try to think positive thoughts about this person. They're working hard at their coursework, and they're getting good grades for it. Good for them. 

I'm really not seeing what A did that pissed you off so badly. They're throwing a party, and invited someone you don't particularly like. 
 
I'm not sure why you see that as inappropriate. Perhaps you should trust the judgement of someone you consider a great mentor?

Grin and bear it.  You will always have to deal with people you don't like.  It is part of life.  B may not even actually show up.  If she does, it is never good to burn bridges, even if you think you will never need them. 
 
Also, I know it hurts to forgive, but try.  You will be better for it, I promise you.  It doesn't mean saying what they did was ok, but carrying a grudge is like drinking poison and expecting the other person to die.

Update:
 
Not sure exactly what happened but my advisor has done a 180. He is friendly, encouraging, smiles a lot now, and overall the relationship is good. This change coincided with my completion of a big project I had been working on as part of my RA duties. He did tell me that I did a really good job and that my work was being shared with others in the department and being utilized in various models.So I guess my successful completion of the project and job well done is what turned things around.
 
Not sure why he was so tense about it before though. Maybe he was receiving pressure from people above his pay-grade that I wasn't aware of, or any number of things. It is just kind of funny though, because I didn't change anything about my attitude or approach with him. I just kept working my arse off and I guess that was the right thing to do. Either way I'm glad things have turned around!

Be honest. People (especially the PI) will be more upset that you lied to them than the fact you changed research groups to get a funded position, which is a great way to burn bridges. Why specifically don't you want to tell them which lab you are moving to? 
 
Just say that a funded opportunity came up in another lab, it is a better fit to your research interests, it's not you its me, blah blah blah. Don't talk about anything negative in conjunction to your current lab either with your current or future lab. Thank your current PI and lab mates for their assistance and how much you valued the opportunity to work with all of them (even if this is an outright lie). You don't have to tell them which lab when disclosing your departure, but expect them to ask and (again) don't lie. The odds are that someone in your current lab will have a connection to somebody in your new lab...or a connection to a connection in your new lab, so they'll find out the specifics anyway. 

How about coming in to work 1 or 2 hrs earlier, before anybody else gets there? That gives you time to set up your own reactions, do your most important tasks, etc before people come along asking for favours. 
 
Putting in earphones and listening to music as you work is a good way to deter casual question-askers.
 
Lastly, don't sweat too much. You aren't expected to be perfect, and everybody understands that it takes a while for new PhDs to settle in and get stuff right first time. 

In most STEM fields, it unfortunately is at the discretion of your PI when you defend your thesis & graduate. In most cases, an email such as you received would not count as a "threat", it is simply a statement of expectations. Although you are adamant here that you don't want or need help, it might be apparent to others that you really do need assistance with your research, which is why they are trying to intervene ("I want to help you" can be an indirect way of saying "You're struggling and you need help."). 
 
At this point, your path of least resistance is to sit down with your PI in person and agree on a timeline for your graduation. Ask them directly what (and how much) work you need to do before they will let you graduate. Write down what they say on paper, then email them a "summary" of what you discussed once the meeting is over. Then go ahead and do that work, even if you don't like it. 
 
Regardless of whether you go into academia or industry as your future career, there will be a lot of times when (i) you have to work with others even when you don't want to or don't think it is necessary (ii) you have to complete more tasks than you want to, either because your boss has told you to, or because need to get grant money, publications or new research projects off the ground. You can't be a successful scientist in a vacuum. 

I think that the main problem is that you're allowing yourself to get annoyed by it. I guess I would question why it is so specifically annoying (are you perhaps a little envious of the online attention they are getting from those posts? is there something else in your grad school life that is giving you stress, and you're offloading your annoyance/frustration onto something/body else?).
 
Instead of being annoyed, try to think positive thoughts about this person. They're working hard at their coursework, and they're getting good grades for it. Good for them.