Knock knock. Who's there? Sherwood.

Sherwood who? Sherwood you let me in, it's chilly out here!

Knock knock. Who's there? Dwayne.

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

Knock knock. Who's there? A door.

A door who? A door has no 'who,' it's an inanimate object.

Knock knock. Who's there? Olive.

Olive who? Olive your jokes are so funny!