What is an arse?

"So, what's an arse?"
... (thought) You are, then saying it.

"No, what is an arse?"
You are.

"No, you see it's a joke."

The sad thing, the would-be joke-teller doesn't understand that being an arse isn't funny, but he's the butt end of a great deal of guff, grief and undoubtedly jokes. Jokes can't tell themselves, so that's his paradox.