Let me first start out by saying that being Indie does not fit into a particular group. Indie stands for Independant, as in on you're own, against social cliques, there for saying, "I am Indie," would defeat the purpose.
An Indie poser is indeed someone who thinks and says that they're Indie. The obviously try too hard by trying to pull of weird colorful looks that just turn out looking gross. An Indie poser probably has no idea about any local or Indie/alternative bands. And if they do, it's obvious they don't enjoy them because they can't speak deeply about the music.
Indie kids do their own thing, they are their own person. They have unique interests and are usually intelligent and pretty deep.
So the kids who are obviously shallow, try too hard, don't care for deep conversations, and hide their true interests... but dress and listen to Indie music and call themselves Indie, are indeed not Indie.
The following is an example of the daily life of a Poser Indie kid trying to fit in:
True Indie Kid: I was watching Donnie Darko last night, and I just realized how fascinating the quality of the cinematography was, and the music choice really reflected the true agony and confusion I felt Donnie was going through.
Poser Indie Kid: uhm... yeah the giant bunny is so fucking.. uhm... rad. I uhm.. really like the... quality.....??
True Indie Kid: Okay man whatever
Bottom line--- If you try to be or want to be Indie, you never will. Because you are not.
Indie Posers are whack and retarded.