An MIT linguistics professor was lecturing his class the other day. "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."
A voice from the back of the room piped up, "Yeah, right."
(https://www.ling.upenn.edu/~beatrice/humor/double-positive.h...)