Why are there no Chuck Norris knock-knock jokes? Because Chuck only has to hit the door ONCE.

*knock knock* whos there? sir theres been an accident. theres been an accident who?

"Knock knock." "Who's there?" "Doorbell repairman."

Knock knock?? Who's there?? Jehovah Witness. Knock knock?? Knock knock?? Hello?? Knock knock??