cat in a bathtub 

Ok first off, I've seen this as dog in the bathtub on this site and it is wrong. Dogs love water, cats hate water. Which is why when you are fucking a girl in the ass and manage to get your nuts up in her too it is called cat in the bathtub. Have you ever tried to keep a cat in a bathtub? It is about as tough as getting both nuts up a girls ass.

I was fucking me Julie in the ass last night and I stuffed my nuts in her ass too. Man, she thrashed around like a cat in a bathtub!

cat in a bathtub by Lebonier March 30, 2005

Cat in a Bathtub 

A sexual act involving trying to push your testicles into someone's anal cavity during non-participatory guy on girl intercourse.
Usually done to try to get more enthusiastic involvement from your partner.

"Man, I was banging Shana the other night, and she was laying there all comatose, so I tried stuffing my balls in her ass... It was like trying to stick a cat in a bathtub..."

Cat in a Bathtub by Turd Ferguson 74 March 5, 2009