I remembered this one recently, probably because I went back to work at the store where someone once got angry with me for sharing it. I guess because it went over his head and that offended him? Or maybe he just didn't like philosophers, or French people. Anyway, here you go.

French philosopher René Descartes went to a pub and sat down at the bar.

"Bonjour, René!" the bartender said. "Will you be having your usual?"

"No, I think not," Descartes replied, and vanished.