Just a lovely little joke...
I just had an argument with a girl i know. She was saying how it's unfair that if a guy screws a different girl every week, he's a legend, but if a girl screws just two guys in a year, she's a slut.

So in response i told her that if a key opens lots of locks, then it's a master key. But if a lock is opened by lots of keys, then its a crap lock.
That shut her up.