Version 1
Descartes walks into a bar and sits down. The bartender asks “You wanna beer?”
Descartes says “I think not.”
…and disappears.
Version 2
A horse walks into a bar. The bartender says, “you’re in here a lot, are you an alcoholic?”
The horse ponders for a minute and responds ” don’t think I am” and *POOF* he disappears.
This is where philosophy students start to snicker, as they are familiar with Descartes and the postulate “I think, therefore I am.”
But telling you that first would be putting Descartes before the horse