Undercover Pooper

Alright, listen up, buttercup. So, you know how a detective is "undercover" when they're hiding their real identity to solve crimes? And "pooper" is, like, a silly word for butt? Well, the joke is that an ass (like a donkey, but also slang for butt) that's a detective is called an "undercover pooper" because it's a play on words that combines the detective term with a childish term for butt. Get it now, smarty pants?