Who's there?
Nun.
Nun
who?
Nun of your business!
Who's there?
Diploma.
Diploma
who?
Diploma is here to fix the sink!
Who's there?
Impatient Pirate.
Impatient Pirate
wh-
ARRRRRRRR!
Who's there?
Major.
Major
who?
Major laugh.
Who's there?
Usher.
Usher
who?
Usher wish you would let me in!
Who's there?
Police.
Police
who?
Police hurry, I'm freezing out here!
Who's there?
Cook.
Cook
who?
Hey! Who are you calling cuckoo?
Who's there?
Doorbell Repairman.
Doorbell Repairman
who?
Ding Dong! My work is done here.
Who's there?
Doctor.
Doctor
who?
You've seen that TV show too?
Who's there?
Police
Police
who?
Police, can I stop telling knock knock jokes!

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