I once had a professor who apologized to our class, confessing that he had given us lectures while drunk. None of us had noticed. He was a brilliant guy, and apparently alcohol just slowed his speech down a bit.
I had an English Lit prof. who ranted on and on about the evils of margarine and how he only ever used butter. I'm assuming he meant in a food-like manner, but no one ever asked. He did this multiple times, and burnt up the better part of the class time doing it.