you what?

Bizarre game. Simple to do, tough to explain. Person A makes statement. You say 'You what?' They repeat statement, and you just double it. An example; A : I'm just going for a shit. B : You what? A : I'm just going for a shit. B : WHAT!? You're going for TWO shits!? You could get out of it by saying 'Just the once' before you spoke. Lasted ages.