Knock knock. Who's there? Pane

Pane who? I'm having a glass-half-empty relationship with you, it's a window of opportunity to change.

Knock knock. Who's there? Door.

Door who? You just said 'who's there?' The door is *right here*.

Knock knock. Who's there? Sew

Sew who? Sew long, I've been trying to weave a good joke.

Knock knock. Who's there? Grape.

Grape who? Grape to meet you, I've heard a lot about you!