Linguistic humor alert

From NewMexiKen:

A linguistics professor was lecturing to his class one day. “In English,” he said, “A double negative forms a positive. In some languages, though, such as Russian, a double negative is still a negative. However, there is no language wherein a double positive can form a negative.”

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

[H/t to Shakespeare's Sister]