The following joke is popular:
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.”
But I wonder how common is the phenomenon. "yeah, right" isn't exactly double-positive, or at least it relies on intonation to convey the negative meaning. However, in Bulgarian "да, да" ("da, da" = "yes, yes") almost always means "no" (still, intonation plays a role).
What other languages exhibit this phenomenon?
The romanian also exhibits this feature. "Da, da", said in a certain way means "in no way" or "never".