A not so new one, but worth a laugh all the time !

A professor of Linguistics was lecturing to an audience about similarities and dissimilarities found among languages. He pointed out that in Russian, the use of a double negative does not alter the intent of the statement but, in English the use of a double negative renders a statement positive. He then pointed out that never does the use of a double positive in English make a statement negative.

A voice from the back of the room shouted, "yeah, right!!!"