Joke: Knock knock!
Who's there?
Howard.
Howard who?
I'm great, thanks for asking.

Joke: Knock knock!
Who's there?
Razor.
Razor who?
Razor hands! This is a stick up!

Joke: Knock knock!
Who's there?
UPS.
UPS who?
... Just UPS, I need your signature.

Joke: Knock knock!
Who's there?
I scream.
I scream who?
What are you? An angry owl?

Joke: Knock knock!
Who's there?
I eat mop.
I eat mop who?
Haha. Gross.

Joke: Hydrogen walks up to Oxygen and says, "You stole my electron!"

Oxygen says, "Are you sure?"

"I'm positive!" replies Hydrogen.