A few weeks back I volunteered to work on a research project (actually, 3) with a professor who is in my department but not my concentration. He has no money to offer, so the incentive for me comes from the potential for publications. Because he has no funding, he has literally no one to help him. I am his only volunteer.
He asked me how much time I could devote, and because I was a stupid and idealistic first year at the beginning of my semester I tentatively said 8-10 hours/week. He agreed and said that anything less than that was "not worth it" that 10 hours/week is the minimum amount of time I could devote. Fast forward a few weeks and my classes, other research team commitments (actually in my area of study) and my assistantship are all heating up. I don't devote much time to this prof (we'll call him Prof X)'s research. I email him with a question about something and he responds snippily "what about the other things I asked you to do?" I ask to meet, I hear no response.
This weekend I receive an email from Prof X asking me to give a presentation to prospective research participants this Wednesday. I reply that I am willing, and I hear nothing from him. Today (Wednesday) I get an email saying "here are the details of the presentation you will make tonight" and just kind of generally orders me around instead of asking me if I am willing to do all this. He also wanted to meet within the hour of sending me the email, when I was not even on-campus. When I responded he ordered me to review the materials for tonight.
I feel like Prof X is being a little overbearing, and not exactly nice, especially considering I am the only one helping him. I know I can't quit (although I do sort of want to). How do I deal with this nicely but firmly? What are my options? Honestly his stuff is low on my list of priorities and just adding stress, especially considering the way he treats me. Advice?