(from a hairstyle popular with the people described, usage invented by Kaecyy in 2005)
A generally amiable but hopelessly nerdy person-- not necessarily possessing an actual ponytail or even long hair-- who is usually immersed in a combination of science fiction and fantasy literature (and their derivatives), roleplaying games (often in their live action varieties), the gothic-industrial subculture, and/or the historical reenactment of pre-industrial periods of European history (often at what are called "Renaissance fairs")-- among other influences-- to or nearly to the point of lifestyle.
You talking shit about Patrick? Fuck you. Yeah so he's a bit of a ponytail, but he's ten times as nice as you. Yeah, YOU'RE one to talk. You've got a ponytail in the closet-- uh-huh, you know I'm talking about that Darth Vader helmet. And the kilt. Suck phaser, buddy.