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 sackmug.
Get the slapping the sackmug. 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 18, 2023
 Get the Slap Sackmug.
Get the Slap Sackmug.