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? Dwayne

Dwayne who? Dwayne the bathtub, I'm dwowning!

Knock knock. Who's there? Sew

Sew who? Sew glad you asked, it's a tailor-made joke!

Knock knock. Who's there? Cows go

Cows go who? No, cows go 'moo'