What's the word when you pretend to be something/someone your not?
The popular word used while I was in high school is "poser".
The word is masquerading which is used when one pretends to be someone or something else. Other relevant synonyms include impersonation, imitation or posing.
An actress? liar? pseudo name? :P
Ambiguity, obscurity, facade, alias...etc.
Hypocrite is right! Don't even think about it. You will screw up everything in your life (and I mean everything) if you pretend to be someone or something you are not. You will also never discover who you really are and what talents you have.