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 man went to the police station wishing to speak...
A man went to the police station wishing to speak with the burglar who had broken into his house the night before. "You'll get your chance in court," said the desk sergeant. "No, no, no!" said the man. "I want to know how he got into the house without waking my wife. I've been trying to do that for years!"