Acronym for Athletic Thanks With A Pat, which refers to the male sporting ritual of slapping some major ass after a big play on the field/court.
"Dude, number 14 totally has the hots for number 45 out there."
"No way! How can you tell?"
"After 45 hit that homerun in the tenth to win the game, 14 greeted him with an extra fat ATWAP, and he didn't hold back on the courtesy squeeze."