This is a repost from 2006. The second one, of course, is the most famous Descartes joke ever.
Descartes walks into a bar, and tells the bartender, "I'm excited about the live entertainment tonight!" The bartender says, "Yeah, the trick pony is pretty cool." "The trick pony! I thought it was Karaoke Night! I was looking forward to it so much." "Well," says the bartender, "we can do that, too." So they got out their schedule and put Descartes before the horse.
Descartes walks into a bar. The bartender says, "Are you having a beer?" Descartes says, "I think not," and ceases to exist.
Descartes walks into a bar, then goes out the back, circles around, and comes back in. He does this several more times, and finally the bartender says, "You're going in circles!" And Descartes says, "Thank God!"
Descartes walks into a bar. Then he says, "Ouch!" You would, too, if you walked into a bar.