A lecture about English
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."

A lawyer returns to his parked BMW to find the headlights...
A lawyer returns to his parked BMW to find the headlights broken and considerable damage. There's no sign of the offending vehicle but he's relieved to see that there's a note stuck under the windshield wiper."Sorry. I just backed into your Beemer. The witnesses who saw the accident are nodding and smiling at me because they think I'm leaving my name, address and other particulars. But I'm not."