Knock knock. Who's there? Anita.

Anita who? Anita little help with these heavy bags!

Knock knock. Who's there? Pecan.

Pecan who? Pecan-der this: it's a nut-terly punishing joke, but I shelled out for the delivery!

Knock knock. Who's there? Philosophically speaking, the notion of a 'who' is a social construct and the concept of identity is fluid, so the idea of a fixed entity on the other side of the door is a fallacy.

Knock knock. Who's there? Cereal

Cereal who? Cereal-ly good at making bad jokes, it's a grain of truth!