Knock knock. Who's there? Dwayne

Dwayne who? Dwayne the bathtub, I'm dwowning!

Knock knock. Who's there? I forgot

who? Oh wait, I remember now, but it's not like it matters because I'm just going to forget again anyway.

Knock knock. Who's there? Hugh.

Hugh who? Hugh-man, I've got a 'Hugh'-ge request: can you 'Hugh'-mor me by letting me in? Because this joke is so pun-tastic, you'll 'Hugh'-rry to tell all your friends, and they'll 'Hugh'-ge-ly regret not being here to 'Hugh'-ear it first!

Knock knock. Who's there? This isn't a door.

This isn't a door who? Exactly, you're knocking on a wall.