I'm not sure why it happens, but I think it all goes back to that "nurses eat their young" mentality. More than likely, they had an instructor that was hard on them, and they feel like passing it on. Like I said, I tried to stay under the radar, so I kept my mouth shut in class. The only time I ever spoke up in front of a teacher if if I was specifically called on. It's different if there are only other students there, like during group projects. Sometimes it was hard - my minor was in genetics with my first bachelor's degree, so when the teacher made a mistake during our genetics lecture in nursing school, I literally had to bite my tongue. It was definitely the safest choice though. You could always see that little switch go off in an instructor's head when they found a student they thought was going to be a problem, and it was almost always a student who had their hand up too much in class, usually accompanied by a somewhat "know it all" or defensive tone to their voice when asking questions.