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."

Bank customer service
"I'm not saying that the customer service in my bank is bad, but when I went in the other day and asked the clerk to check my balance ... she leaned over and pushed me."