At the first session of a conversion class...
At the first session of a conversion class the minister conducting the class asked, "What must we do before we can expect forgiveness from sin?" After a long silence, one of the men in attendance raised his hand and said: "Sin?"

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."