Knock-knock. Who's there? To. To who? No, to whom.
Q: Why can't you tell blondes knock-knock jokes? A: Because they leave to go answer the door.
Two kittens on a sloped roof. Wchich one slides off first? The one with the lowest mew.
Knock, Knock! Who's there? D umbbell. Dumbbell who? Dumbbell doesn't work so I had to knock!
Chuck Norris was once part of a knock knock joke. The Joke ended abruptly when after the first knock the door blew up killing the man behind it.
Q: What do computers and air conditions have in common? A: They're both become useless when you open windows.
"Have you heard my knock-knock joke?" asked the blonde. "No," said the brunette. "Okay," said the blonde, "you start."
Q: 0 is false and 1 is true, right? A: 1.
Knock Knock. Who's There? Justin. Justin who? Your justin time to wipe my ass!
Knock Knock! Who's There? Figs Figs who? Figs the doorbell, it's broken!
Knock, Knock! Who's there? Doctor Doctor who? That's a great TV show, isn't it?