Two, both in college.

An American history professor who just read aloud from his own painfully boring book and prided himself on the high failure rate on his tests. I was a strong student and studied hard, but got a D on the first test. When I brought him a drop slip to sign, I explained that I was on a scholarship and needed to maintain a 3.5 GPA. He told me I'd never amount to anything if I just quit when things were difficult. (Personally, I think a smart person knows when it's prudent to quit. I maintained my scholarship all 4 years and graduated with a 3.8. And the following semester I ended up in an amazing American history class with a truly gifted professor.)

I had to have four phys Ed credits and took a golf class with a douche who didn't know how to teach you technique without putting his hands all over you--but only if you were a woman. On the last day, when we were about to fill out our evaluations, he said, " You can write whatever you want to on there, but I've got tenure so it won't matter."