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."

Bang Bang!
Q: What goes, "clip clop, clip clop, bang! bang! bang!
clippity clop, clippity clop?"

A: A drive by shooting in an amish neighborhood!