Descartes is sitting in a bar, having a drink. The bartender asks him if he would like another. "I think not," he says and vanishes in a puff of logic.
I've seen this attributed to the USAF, Quantas, and the Marine Air Corps. Personally, I think they're too perfect to be real, although my buddy Steve (who was a Marine pilot and AvTech) sez these are plausible.
Probably a sign of my misspent youth, but I know that nothing good can come from a project where Japanese scientists drill towards the center of the earth.