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 rabbi, a priest, and a lawyer were all...
A rabbi, a priest, and a lawyer were all caught in a shipwreck. Naturally, there are a lot of sharks circling around. All of a sudden, one shark darts in and grabs the priest for lunch. No more priest.
The rabbi starts praying frantically, but to no avail, as a shark comes in and eats him, too.

Now the lawyer is really worried, as a shark is coming for him. But, miracle of miracles, the shark puts him on its back, carries him to shore, and lets him off.

The lawyer, curious, waits till the shark is far enough away not to eat him, and asks, "How come you didnt eat me?" And the shark replies, "Professional Courtesy!"