Does not exist. If it did exist; the definition would be 'someone trying to be a certain stereotype'. However, most people define it in their heads as 'someone who isn't whoever/whatever they are trying to be because; 1, if they have to try then they are fake, or 2, they are trying too hard and failing'. Both of these reasons are judgmental and highly unintelligent. If using the word to refer to someone else, the user is generally saying it to make themselves feel higher than the other because the user feels insecure or low. What the word, in all honesty, really is? A lie.
Insecure 1: "Look at that girl. She tries so hard to be scene. What a fake."
Insecure 2: "Seriously. She fails so bad. What a poser."
Intelligent Life-form: -laughs- "Its funny because I know that the only reason you're saying that is because you're trying to make yourself look better. It's also funny since the only reason you're doing that is because you're insecure about your own self. -laughs- ...and you say she fails."
By Teckadoll