With Szwagier, Yellow Duck and Zola all keeping a wary eye open for burrow solecisms, we have been hesitating whether or not to post this one - but have decided to take the plunge:
A linguistics professor was lecturing the class.
"In English," he explained, "a double negative forms a positive. In some languages, such as Russian, a double negative is still a negative."
"However," the professor continued, "there is no language wherein a double positive can form a negative."
Immediately, a voice from the back of the room piped up: "Yeah..... right...."