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."

Anniversary
A guy says, "For our Twentieth Anniversary, I'm taking my wife to Australia."

His friend says, "That's going to be tough to beat. What are you going to do for your Twenty-fifth Anniversary?"

The first guy says, "I'm going to go back and get her."