Knock knock. Who's there? Pane

Pane who? Pane-de-monium, I'm having a window of opportunity to tell you a glass-half-full joke!

Knock knock. Who's there? Candice.

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

Knock knock. Who's there? Continue.

Continue who? Continue the joke. That's the whole thing. No pun.

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.