Noun, The guy in prison that keeps stuff (sometimes cell-made weapons) up his ass for safe storage.
"I don't remember which keister bunny has my 2 dollars, but I'll probably never get it back now"
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prison guy1: "I made a knife out of the end of my toothbrush"
prison guy2: "Where is it?"
prison guy1: "I gave it to the keister bunny in cell 5"
Urban legend: An imaginary entity/being not unlike Santa Claus or The Tooth Fairy who visits faggots when they're sleeping, takes their ass cherry and then leaves them a shiny new quarter.
A. "Look at THAT fucking fruitloop."
B. "What...he's GAY?"
A. "If that guy didn't get a visit from the Keister Bunny, then I don't know who did..."
The Keister bunny ended up spending the three dayholiday in a special"filming cell" outfitted with cameras. the cell is used to video training films for cell extractions, finding contraband,etc. for the holiday, it is being used to add to the popular PUSSYASS TRAINED TO BE A PRISON BITCH SOLD TO THE CRIPS VOLUME 3: FACE FUCKING NO HOLDS BARRED.