This Might Have Continued Indefinitely Had It Not Been for the Robbery

Customer: Hi, I'd like a ham and cheese sandwich, please.
Deli worker: We're out of roast beef.
Customer: A ham and cheese sandwich, please.
Deli worker: I told you, there's no roast beef.
Customer, slower: A sandwich with ham and cheese?
Deli worker: But there's no roast beef.

--Broadway & Exchange