One day a man heard knocking at his door. He opened the door only to see a small snail sitting there smiling. The guy picked the snail up and threw it as far as he possibly could. Three years later he heard knocking at the door again. He opened the door to see the snail. The snail said, "What the hell was that all about?"
Knock, knock. Who's there? Kanga. Kanga who? Actually, it's kangaroo!
Knock, knock. Who's there? Owls say. Owls say who? Yep, that they do.
Who do you think would win in a fight? Godzilla or King Kong Neither, Chuck Norris doesn't let his pets fight!
What is a chameleon's motto? A change is as good as a rest.
"Have you heard my knock-knock joke?" asked the blonde. "No," said the brunette. "Okay," said the blonde, "you start."
Knock, Knock! Who's there? Doctor Doctor who? That's a great TV show, isn't it?
Fast way to screw up someone's Knock Knock joke...? "It's open."
Why do milking stools only have three legs? 'Cause the cow's got the udder!
Knock-knock. Who's there? To. To who? No, to whom.
Knock, Knock! Who's there? D umbbell. Dumbbell who? Dumbbell doesn't work so I had to knock!