Two men walk into a bar.

This little gem plays on one of the most famous joke setups in existence. Our brains are instantly primed to picture a tavern, a couple of stools, and a friendly bartender. The setup leads us down a familiar path, expecting a clever conversation or perhaps a talking parrot. But the punchline yanks the rug out from under us by revealing the "bar" isn't a place for drinks—it's a solid, unforgiving piece of metal.

The humor is a classic bait (Review)-and-switch, a form of wordplay that hinges on the double meaning of a single word. It's also a perfect example of an "anti-joke," which gets its laugh by subverting the structure of a traditional joke. Instead of a witty dialogue between the two men, we get a simple, slapstick image of a third, less observant person about to get a headache. It’s a brilliant, simple pun that works because it's so unexpectedly literal.