Knock, knock; Who is there? Love; Love who? U, U, U!
Knock knock Who's there? Double. Double who? W!
Knock,Knock, Who is there? Pen! Pen who? is...
Knock, knock! Who's there? Spell. Spell who? W-H-O.
Knock-knock Who's there? Fuck. Fuck who? You.
Fast way to screw up someone's Knock Knock joke...? "It's open."
Knock knock! Who's there? Yah! Yah who? Naaah, bro, I prefer google.
Knock, knock. Who's there? Owls say. Owls say who? Yep, that they do.
Knock-Knock Who is there? A long penis with a naked head. Come in please we were waiting for you.
Knock-knock Who is there? A shattered penis with many diseases. What kind of illness? Gall, Aids, Gonorrhea, Syphilis... Enough, it is the best present for my mother in law.