I do have to say that I've seen a FEW teachers who were just downright STUPID, MEAN and RUDE to their students.
What to do:
MEAN - If he/she is just "mean", stay out of his/her hair because they generally just don't have a sense of humor and don't want to put up with your silly nonsense and won't mix words with you when talking to you.
RUDE - No big deal if it's only occasional; however, if there are consistent insults, report it to those in charge. Nobody should have to sit through that. Teachers whom I've seen that are consistently insulting students are very often the ones below... STUPID.
STUPID - And I do not mean occasionally or even often ignorant about something, I mean just plain, downright STUPID. There aren't that many, but believe me, they're out there, and every teacher, parent, administrator, student should do whatever it takes to get them FIRED for incompentence. I don't know how they got through college unless somebody else did their work for them and/or took tests for them, but, whatever, they should be washing dishes, not teaching. ETA I'm talking about SEVERELY RETARDED, and, YES, I've seen them in the classrooms. They usually/often use insults and cruelty to cover up their inadequacies or some are just NICEY-NICEY who just LOVE their students (bull).