It's also a very good idea to NOT tell a Chef his food probably sucks BEFORE he cooks it for you.
Hawwwwwwwwwwwwk.......spit.
Know what I mean, vern?
Another myth. I have worked in many restaurants, and that just is a flat out myth. I worked my way through 6 years of university working in restaurants.
I have also worked as a university professor, as a teaching fellow in graduate school, and have worked and associated very closely with professors and other university teaching staff. Most just don't have the thoughts to spare taking out some sort of revenge or acting out a vendetta on an unpleasant student or a student who has disagreed with them. I know because I've been there: you have so many papers to read, you don't pay any attention to the name on the paper until you have finished grading the paper and have to record the grade. There just isn't time, and for most professors, there simply isn't the will to make an issue of an unpleasant student by giving him/her a bad grade.
As well, any student who believes a grade to be unfair can go to the department chair and make a formal complaint. If the student still feels he/she is not being treated fairly, he/she can go to the college administration and make yet more complaints.
Professors are not there to take out personal vendettas on students. They just don't care about it the way students do. They don't take it personally the way students do.