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Latest case: Greenlighting.

Greenlighting was a roughly three-day-long attempted internet hoax launched by Something Awful users on the evening of July 2, 2005, primarily as references to the greenlighter message board or as postings on said board. The hoax referred to a new sexual practice in which men and women wore green shirts with the collars turned up, and had sexual relations with whomever turned the collars down. In truth, no such sexual practice has taken place on any notable scale. The practice was invented in an attempt to imitate the success of the Toothing hoax of 2004.

Previously on "Don't believe everything you see on the Internet:" Toothing.

Toothing is a media hoax which claimed that Bluetooth-enabled mobile phones or PDAs were being used to arrange sexual encounters.

It appears that toothing started around March 2004, in the form of a fake forum designed by Ste Curran, then Editor at Large at games magazine Edge. On April 4, 2005, the creator of the forum admitted that the whole thing was a hoax.

Toothing was described as the possibility to leverage the ability of a Bluetooth device to 'discover' other enabled devices within a radius of around 30 feet (10 meters). Having discovered another device, the expression toothing? would normally be sent as an initial greeting.

Amusingly, "toothing" was apparently shown on a CSI Miami episode. As if I need another reason to dislike the CSI/Law & Order TV show genre.

Speaking of reasons, story via Reason's Hit and Run