A friend of mine was giving her BF some head once and he said something to piss her off. I can't even remember what he said because what she did totally trumps everything.

She bit him in the balls. He couldn't walk right for days. They broke up a few months later, but because I have a big mouth and I told pretty much everybody in our circle of friends, he's still known as "the guy who got his balls bit by Jen".

Note to men -- when you girl is giving you a blow job, don't piss her off. Teeth are very powerful.