The term 'greenlighting' refers to a secret fashion code that sexually promiscuous teenagers use to communicate with each other. Greenlighters wear green shirts with the collar turned up. When they see someone else wearing a green-collar-up shirt, they pull their collar down. This is the secret signal that means 'let's have sex'. The other person then signals their willingness by pulling their collar down, in turn. If they're not willing, they keep their collar up (which is called 'redlighting').
Of course, this secret fashion sex code isn't real. It's a hoax (or rather, an idea for a hoax), dreamed up by some people at WookieFetish.com. The idea was that they were going to fool the media into believing that this practice was really going on... just as the creators of the toothing hoax
had done a year or so ago. But unfortunately for the WookieFetish crowd, their hoax got exposed before it had a chance to gain any momentum. Cyrus Farivar (an editor at MacWorld) outed it on his blog and also via a wikipedia entry. In an article on Salon.com
Farivar tells how his exposure of the hoax then incurred the wrath of the would-be hoaxers, resulting in a few threatening emails and phone calls.
Actually, it doesn't sound like the WookieFetish people ever really threatened Farivar that much. I remember that after I exposed the 'Great UFO Hoax'
being plotted by LUE (actually, I simply reported that it had already been exposed, but that distinction was lost on them) a few of them threatened to send thousands of empty boxes to my house. Strange threat, but nothing ever came of it.