I had an anthropology professor who HATED it when people would leave his lecture early. One day a suddenly got up from the front of the class and made a b-line for the door. The professor yelled "I CAN'T BELIEVE YOU STUDENTS, THIS KIND OF BEHAVIOR IS SO DISRESPE----." Right then the girl turned around, looked at the professor, and projectile vomitted.
Another time, I was in immunology and the professor was talking about doing hybridoma in hood. This reminded me of a resent event in the lab where I work, so I started telling my friend about it. A moth flew into our sterile tissue culture hood and the professor freaked out. He spent the next 10 minutes trying to get it out of the hood without contaminating it by dousing a yardstick with 95% ETOH and swinging it around. By doing so, he knocked over all the culture media and was completely ineffective. This made the prof even more upset, and eventually he threw the yardstick down, opened the hood, and smashed the moth with his hand. Everyone in the lab was stunned, as this was obviously not sterile. He turned around and said "WELL IT'S MY LAB AND I ****ING DON'T WANT MOTHS IN IT..... (akward pause for a few seconds) besides, the hood was already contaminated anyway" and stormed off. My buddy starting laughing and the immunology professor lost it. "OK, you two, stand up. I'm up here trying to share some of my knowledge with you guys, so now you're going to do the same. Tell everyone what it is that you're talking about." So I did and the class (including the professor) errupted in laughter. The immuno prof responded with "well, at least you were talking about science," and continued the lecture.