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"
The keyster bunny is the lucky prisoner who goes on work furlong or gets a pass for a family emergency. He then shoves all the drugs he can find up his ass and then gives them to his buddies back in the slammer.
Everybody feels its easter, but the eggs came from the keyster.
Come up on a sharp and some smokes, loc--the keyster bunny came early this year.
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 newquarter.
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..."