Swoop
Verb: The act of dating or hooking up with your friend's EX girlfriend with or with out his consent. Whether it be his/her most recent or one from their past. Not to be confused with Supaswoon where you hook up with multiple EX's in a short amount of time.
"hey bro, remember that girl from the bar that you dated?"

"yeah, what about her?"
"consider it swooped!"