An ultra-stereotypically gay man.
Which is to say: a swishing and mincing, limp wristed, lisping, effeminate queer.
A nelly queen can't stop this behavior, and acts this way around both straight and gay people: they are thought to have been born out of the closet.
Many gay men avoid associating with "nellies" because they actually don't naturally act that way, and they don't want to be associated with the stereotype.
"What were you doing hanging out with that nelly queen last night? What happens if you run into him at the store or something?"
(Referring to a nelly) "Hey, I can tone down the fruit at work, and turn it up at the club, but that asshole's just embarrassing!"
Just as 666 is supposedly the number of the Anti-Christ, 333 is the number of the Semi-Christ. Occasionally seen on bumper stickers and their ilk.
On button or bumber sticker:
"667-the Neighbor of the Beast"