And what no one has mentioned is the situation in which a guy get's drunk and then a girls comes on to him.
Ever woken up to find a girl in your bed that you vaguely remember from the night before? If this happens to a guy, and he's ashamed of what's happened- you don't see him running around saying the girl raped him. But if the situation was reversed, a lot of girls do just that.
So at the risk of sounding like a jerk, that's why it's always best to let the girl give you a BJ before having sex with her. That way if she pulls the whole, "I was too drunk to remember" line, then you can reply with the "you wern't too drunk to play-the-pipe for twenty minutes before hand.
I lived in a fraternity house for a year, so I've heard some pretty screwed up stories that have arisen from just this.