To black-out is to profess your admiration for a girl, only to reject her advances at that crucial moment. To forgo "sealing the deal". The art of being a poser, but not a closer.
Guy 1 - "Hey dude, I almost scored with that girl last night"
Guy 2 - "Yeah bro, we could have totally eiffel towered her if you didn't black-out"
Guy 3 - "You're such a pussy"
Guy 2 - "Next time you black-out, don't drop your gay card"