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 March 20, 2018
A Slap Sack is a place where women keep their fond, sexual memories, so she can think about them while masterbating.
by Mazzy Scarlett December 19, 2023