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 truck driver who had been delivering radioactive waste...
A truck driver who had been delivering radioactive waste for the local reactor begins to feel sick after a few years on the job. He decided to seek compensation for his ailment. Upon his arrival at the workers' compensation department, he is interviewed by an assessor. Assessor: I see you work with radioactive materials and wish to claim compensation. Trucker: Yeah, I feel really sick. Assessor: Alright then, Does your employer take measures to protect you from radiation poisoning? Trucker: Yeah, he gives me a lead suit to wear on the job. Assessor: And what about the cabin in which you drive? Trucker: Oh yeah. That's lead lined, all lead lined. Assessor: What about the waste itself? Where is that kept? Trucker: Oh, the stuff is held in a lead container, all lead. Assessor: Let me see if I get this straight. You wear a lead suit, sit in a lead-lined cabin and the radioactive waste is kept in a lead container. Trucker: Yeah, that?s right. All lead. Assessor: Then I can't see how you could claim against him for radiation poisoning. Trucker: I'm not. I claiming for lead poisoning.