Knock knock. Who's there? Candice.

Candice who? Candice door open? I'm getting board waiting!

Knock knock. Who's there? Lettuce.

Lettuce who? Lettuce *pray* this joke *grows* on you, I've really *leafed* through a lot of ideas to *cultivate* this *gem* just for you, so please *romaine* here and enjoy!

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? Vaughn.

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