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."

An anti-bat spray
Three Pastors from the south were having lunch in a diner. One said, "Ya know, since summer started I've been having trouble with bats in my loft and attic at church. I've tried everything-noise, spray, cats - nothing seems to scare them away. Another said, "Yea, me too. I've got hundreds living in my belfry and in the attic. I've even had the place fumigated, and they won't go away." The third said, "I baptized all mine, and made them members of the church... Haven't seen one back since!"