Your Nan

Alright, listen up, buttercup. So, it's a knock-knock joke, right? Someone says, "Knock, knock." Then you, being the slowpoke, ask, "Who's there?" Then comes the punchline: "Your Nan." And the clueless dude replies with, "WHAT? MY NAN IS DEAD!" It's funny 'cause they thought their nan was at the door, but SURPRISE! She's pushing up daisies. Bet you didn't see that coming, did ya?