To stick an item usually a penis inside another's butt; commonly found in most imageboards, forums, public restroom walls, 4chan, etc., also usually accompanied with the picture of an angry japanese man shouting into a phone.
A: "I just met this girl recently, but I don't know what to do with her. What should I do?"
An ass that is even flatter, and even more embarrassing than a poohbutt. The absoluteworst type of butt to have, or to look at. It practically tilts inward.
Man A: “Look at that poohbutt!” Man B: “No, dude, that’s a pooterbutt right there.”
“Omg, Becky, would you call my complete lack of having any ass a ‘poohbutt’? Or is it a ‘pooterbutt’?”