A girl who you think about when you whack off but don't actually have the balls to talk to.
Ex 1. Man I wish I wasn't a pussy and I could talk to katie, but for now she is my 5-minute crush.
Guy 1: "Man I totally had a 5-minute crush on that girl last night."
Guy 2: "Go talk to her, man."
Guy 1: "Nah I don't have the balls, besides, it's weird now."