Tiki Humor

“In English,” he said, “a double negative forms a positive. However, in some languages, such as Russian, a double negative remains a negative. But there isn't a single language, not one, in which a double positive can express a negative.”

A voice from the back of the room piped up, “Yeah, right.”

“the linguist was the Oxford professor J.L. Austin, and the zinger was delivered by a fellow professor, Sidney Morgenbesser of Columbia.”

via Reddit.