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 judge, bored and frustrated by a lawyer's tedious argument
A judge, bored and frustrated by a lawyer's tedious arguments, had made numerous rulings to speed the trial along. The attorney had bristled at the judge's orders, and their tempers grew hot. Finally, frustrated with another repetition of arguments he had heard many times before, the judge pointed to his ear and said, "Counselor, you should be aware that at this point, what you are saying is just going in one ear and out the other."

"Your honor," replied the lawyer, "That goes without saying. What is there to prevent it?"