in the grocery store

me: We need to think some sort of joke along the lines of, "what's more useless than a Chinese cop?"
Claire (looking slightly puzzled as she inspects a bag of milk): They can't be that useless. There are like however many million of them.
me (long pause, furrowed brow, then comes up with suitable punchline): "I don't know but I bet it's pretty useless."
Claire: Yeah, in my bed, certainly.
me: I said, "cop" not "cock."
Claire: Oh. That too.