A conceited person; a narcissist
This term isn't used to refer to someone with Narcissistic Personality Disorder (NPD).
Warning: usage of this word makes you look like an idiot if female, or like a douchebag if male. In any case of gender, this may cause the reaction of "what the fuck?" to appear.
Girl 1: OMG I absolutely ADORE my hair right now, it's teased just the right way and I didn't even have to put in more than two hours on it this morning!! Did I mention I have SUCH a great bod! I'm GORGEOUS!
Girl 2: what a narcy.
Girl 1: OMG NO IM NOT, BITCH!
Girl 3: WTF?