I've been in college and also vocational schools. The vocational school instructors were worse, perhaps because they weren't as professional. They definitely had biases. One instructor was even asking his female students out on dates and getting mad when they weren't interested. In one case, he asked out a married student and harassed her when she said no repeatedly. I had problems with this same instructor (although he didn't ask me out), and eventually we all realized this guy had serious problems. Let's face it, teachers are only human and they can have the same problems as anyone else. I also had a female instructor in a nurse aide program at a local college: she was biased against older students, but with young students, she would be motherly toward them and encourage them. With the older students, she would roll her eyes at us and make sarcastic comments. She started nit-picking at things we did during the clinical training at a hospital. We realized she was trying to grade us down.
I want to be able to identify problem professors early on, so that I can manage my relationship with them. I did not at first realize these instructors had personal issues, and I was blind-sided. I really don't have much background in human psychology.