One of my favorites, and my BF didn't get it D:
A horse walks into a bar and the bartender says "why the long face? Are you depressed?"
The horse replies "I don't think I am"
At which point, the horse promptly disappears.
Now, if you're at all familiar with the works of Rene Descartes, you're likely chuckling at this point, knowing his famous quote "I think, therefore I am"
But to tell you that first would have been to put Descartes before the horse.
