To be attempting to get with one of your friends past girlfriends,a girl he is talking to, or a girl he is currently fucking. makes you a pwerdan.
If two guy friends sit down at a computer and one of them checks his myspace messages and there is a message from the other guys ex girlfriend, the friend that its his ex would say, uh huh? Pwerdan!
By calling him pwerdan is a nice way of saying,i just busted you tryin to talk to one of my ex's etc...