I can't recall where these originate (cit. req.)

A linguist's joke:

Knock knock.
--Who's there?
Objective case.
--Objective case who?
No, objective case *whom*.

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Frappe, frappe.
-- Qui est la?
Loss
-- Loss qui?
Oui, frappe, frappe! (Knock knock)

====================

and to be faintly music related...

Knock! Knock!
--Who's there?
Caprice.
--Caprice who?
That's show biz...

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and so to bed.