Knock knock. Who's there? Anita.

Anita who? Anita little help with these heavy bags!

Knock knock. Who's there? The joke.

The joke who? The joke who was supposed to be original and unexpected, but now feels like it's just pointing out its own existence.

Knock knock. Who's there? Wu

Wu who? Wu don't know, I'm having an identity crisis!

Knock knock. Who's there? Cows go

Cows go who? No, cows go 'moo'