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 staged wedding to bust dealers
As supposedly reported on CNN:

Undercover police, staging the wedding of "a drug kingpin's daughter", let it be known on the street that dealers were "invited" (i. e. Expected to attend).

The bride and groom were police, as was the band, bartender, and about half the guests. The band playing at the wedding was "S. P. O. C." (COPS, backwards), and the wedding went through the full ceremony, including the dancing afterward.

The long-sought dealers were arrested after the "band" took their break. The last song the band played before taking its break? "I Fought The Law, And The Law Won"