Best. Joke. EVER.
A man walks into a bar
OUCH!!
Traditionally, jokes start with a phrase like "a man walks into a bar..." just to orient the listeners. A man walks into a bar. He asks the bartender, "Do you have any helicopter flavored potato chips?" The bartender shakes his head and says, "No, we only have plane."
Obviously, the bar has nothing to do with the joke, but you need that carrier phrase to alert your audience that a joke is coming. But this joke (perhaps even an anti joke?) short-circuits the listeners expectations, making the intro the punchline. Unless you have a horror of puns, you should at least chuckle the first time you hear one of these jokes. But because many of us are extra-dorky, there's a good chance that you will hear it more than once, in one of its many forms.
Two guys walk into a bar ... the third man ducks!
A magician walks down the street and turns into a bar.
Of course, it doesn't stop there. Now that we have set up a new, unbearably corny standard to geek out over, nothing will do but that we elaborate on it endlessly.
143 lemmings walk into a bar.
Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ow!... Ow!... Ouch!... Ow!... Oi!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... ... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!... Ow!... Ow!... Ouch!... Ow!... Ouch!... Ow!... Ow!... Ouch!... Ow!...
My personal favorite, and quite possibly the worst attempt at a joke ever, is quite simply Un hombre entra en un bar... ¡Ay! Of course, your tastes might lie in other directions -- such as the maximally milquetoast "A limbo dancer walks into a bar. He lost." or the re-punned "A ballerina walked into a barre". However, if you find yourself unwillingly cornered by painful bar puns, there is a recommended response:
"A man walks into a bar, walks up to the bartender and says 'Ow!'. And the bartender hits him for being a weasel faced arsehead."