Knock knock. Who's there? Vaughn.

Vaughn who? Vaughn voyage! Hope your journey's ship-shape and full of bon-bons!

Knock knock. Who's there? Oblivion.

Oblivion who? *everything ceases to exist*

Knock knock. Who's there? An incomplete thought.

An incomplete thought who? An incomplete thought about... what was I saying?

Knock knock. Who's there? The premise.

The premise who? The premise for a knock-knock joke needs two people, and I'm talking to myself.