Punching your hand inside someone's asshole and then you open the asshole and tickle the inside.

The sensation feels like rats crawling up your ass, hence the name.
Nick (you, a kinky motherfucker): "Man, Lisa just gave me rats up my ass."
Mike (your childhood friend who respects you very much, up until this information which has entered the neurons in his brain matter): "What the fuck?"
by miahh June 6, 2022
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