Got this one in my mailbox:

A linguistics professor was lecturing to his English 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.”

Although I dislike ‘funny’ FW: mails I liked this one, and I’ll share! But not trough mail :-)