A closet dork is someone who is socially accepted; however, when they are out of the public eye they conduct activities one would consider unpopular. (Public eye meaning anyone who is socially accepted. The closet dork may still associate with other dorks behind closed doors)
Closet dorks do not fit the stereotypical "look" of a dork, nerd, geek, etc. They generally are able to fit into any "group" of people. Ways to discover if someone is a closet dork may be the usage of vocabulary that your ordinary social butterfly may not understand or Dungeon and Dragons books mysteriously observed sitting around in their residence.
Closet dorks are generally attractive to semi-attractive dorks/geeks. This is part of the reason why they are accepted into popular crowds. It is very difficult for a unattractive dork to become a closet dork.
Closet Dork: Sorry guys, I'd come out with you tonight but I have to take this one girl I just met to the movies.
Popular Friend: He's full of crap. "The reason he isn't coming out tonight is because he's a closet dork and there's a World of Warcraft tournament tonight that he always plays in."
Some of the following qualities usually can be applied to the closet dork:
plays video games, plays at least one sport that requires physical activity (cards do not count), reads "real" books, reads maxim/playboy, invited to parties, throws parties, nice personality, found attractive by attractive females, makes conversation that that people can relate to, has their own stories to tell as opposed to other people's stories/made up ones, can talk about good movies/games, can talk about sports/knows the rules, has a good sense of style as opposed to all vintage/mother bought clothing, do not use woman yet still enjoy sex, and you must be an intelligent person or speaker.
Many Fraternity brothers are considered closet dorks. A "dork" going to college far away from home and learning how to be "popular" as well as a different person. When social events are planned the closet dork presents himself as a "jock like" individual when he really is the definition of a dork behind the scenes. Once this is learned then one can consider himself a closet dork.
*If you are not sure if you are socially accepted or a dork and you are not considerably smart then you should refer to the word "loser". This may apply to you; therefore, strive to attain the aforementioned qualities. It can only get better from here.*