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 boy comes home from school and tells his mother...
A boy comes home from school and tells his mother that he got a part in the school play. "What part?" the mother asked."I play a Jewish husband," the boy replied. "Go back to school and tell your teacher that you want a speaking role!"