A game typically played in large crowds in which you grab random guys' asses and nonchalantly keep walking/doing whatever you were doing. Give your friends a heads up so they can laugh & give you a report. Causes confusion & is hilar when done right.
If confronted: deny it with repulsed look on your face.
Nicole: Dude it's 2:25, the bars are about to let out. We should play a round of grab ass.
Kaitlyn: Hell yeah, look at that one, it's just asking to be grabbed.
(Everyone exits; most likely drunk)
Megan: (Grabs a hand full of ass)
Random Guy: WOAHHH, what the...? (snaps head around, confused, possibly thinking it was the person behind him)