A Two Time
Going to one party, then leaving halfway to go to another one because you're too selfish to stay and have fun with your friends.
I was at the party, but I had to leave halfway to go to the other one. I'm the worst friend ever!
She left the birthday party to go to the concert. I'm surprised she didn't leave to go to the movie too.
He left the cookout to go to the football game. He's a two-timing party animal.