A horse walks into a bar, and the bartender says “Would you like a pint?” The horse says “I think not!” and disappears.
Of course, for this joke to make sense you need to be familiar with the French philosopher René Descartes, who said “I think therefore I am”. The horse thought not, and therefore wasn’t.
I could have explained that before the joke but I didn’t want to put Descartes before the horse!