One who sneaks quietly into a restroom. Waits until your done taking a dump, and then sneaks into the stall and snatches your dump RIGHT out of the toilet before you have a chance to flush. God only knows what the poop thief does with the dump once he steals it.
John: Duuuuude. I think a poop thief just stole my shit.
Anthony: No way??
John: yeah, one second it's there, the next its gone. o.O