I had a teacher go off on a tangent about why Star Sex: The Search for Sperm was his favourite pornographic parody film, mostly due to the 'clever' puns.
"It was very clever, because instead of Uhura, they had U-whore-a. And Captain Kirk was Captain Cock. No, really boys, it was really good."
Meanwhile the whole class just sat there staring at him like... well, like he'd just broken off from teaching to tell us about his favourite porn.
There was also one time we were discussing Bond fims, and he did an impression of Sean Connery saying "Miss Funnyfanny", adding "Because you would, wouldn't you? If you had a teacher called Miss Moneypenny, you'd call her Miss Funnyfanny, wouldn't you? You would!" Again, a lot of staring from the class.
He'd also gone to university with another teacher at the school, and used to act out his (highly dubious) stories of the adventures they had together. These always involved his putting on an extremely over the top Welsh accent for the other teacher's lines, and most of the stories would end with the two of them having a fight. (which naturally our teacher always won)
He was a very strange man.