When someone with a tiny penis "try's" to masturbate. Their peter is so tiny that they end up just slapping their sack
Jessica: I caught Perry beating off in the bathroom yesterday.
Amanda: Trust me, his dick is so small he was just slapping the sack.
Amanda: Trust me, his dick is so small he was just slapping the sack.
by Jameshasahugecock May 13, 2018
Get the slapping the sack mug.