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."
To be fair, "yeah, right" is a sarcastic statement and linguistically the two words do not scope eachother so the positive statement is produced at the pragmatic level, double negatives are syntactico-semantic.
A voice from the back of the room piped up, "Yeah, right."
(https://www.ling.upenn.edu/~beatrice/humor/double-positive.h...)