The actual term that I think should be used towards someone who thinks that they are something are not is: 'A begg' this means that the person is trying to live up to something that is impossible for them to achieve.
numerologist
Paranoid
Someone who thinks that being a hipster is to mainstream can be referred to as a jazz-maniac.
that's a hypochondriac.
paranoid
A self-centered person or egocentric individual is someone who thinks the world revolves around them.
You could call them "arrogant" or "overbearing."
A know-it-all!
God
That was a terrible question, because you call someone who thinks they are ill all the time a hypercondriac. So as in Jeopardy, "What do you call someone who is constantly under the impression that they are ill?" Answer: "What is an a hypercondriac?" That is correct!
you call them able?
you call them able?