Ambiguous Disorder: Seems to have Borderline Personality Disorder (in addition to his narcissism, sadism, and sociopathy), as this would explain his hallucinations as well as some other things he reports, such as identity disturbance, his mood swings, and his tendency to not feel much of anything.
Cloudcuckoolander: Hallucinates that an ATM tells him to feed it a stray cat. He actually tries to do it in the movie.
Evil Is Petty: Almost all of his murders are motivated by people having nicer clothes or better apartments than he does.
Hallucinations: Caused by stress, and extremely bizarre, but he believes every one of them.
Inferiority Superiority Complex: Despite his insane levels of narcissism, it is shown often that Bateman utterly detests himself as much as he does everyone else and most of his murders are motivated by people unintentionally reminding him of this.
It's All About Me: The only people he refuses to kill are ones who profess some affection for him, all of which he coldly discards.
Karma Houdini: He escapes punishment for all his crimes, and boy is he upset about this status.
Morality Pet: Luis and Jean. Not only are both in love with Bateman, they're also the only two characters in the story who are genuine people and completely honest. Consequently, Bateman can't bring himself to kill either of them, and actually is somewhat nice to Jean - definitely far nicer than to any other woman he knows.
Pet the Dog: In the book, he drops a dollar bill into a homeless girl's cup to see if he's capable of doing something good. It's subverted since the girl was a student and the cup was full of coffee.
Pop-Cultured Badass: Some chapters consist entirely of him going on tirades about music, be it Whitney Houston, Huey Lewis, or Elvis Costello. Subverted, at least with Whitney Houston, since he's convinced she's a jazz singer.
The Sociopath: Informs everything about his life — the film's director describes him as a Martian trying to imitate human behavior (and never quite hitting the mark). He is probably one of the best examples in media.
Tall, Dark and Handsome: As we learn during his narration of his morning routine, he is the pinnacle of physical perfection.
Villain Protagonist: A Serial Killer with a host of disorders making him Ax-Crazy. Our central focus, everyone. And even if he's just imagining the murders, he's still an unlikable, self-centered, elitist, racist, shallow bastard.
Would Hurt a Child: He stabs a small boy to death just to see if he'd enjoy it. He doesn't... because he doesn't find it evil enough.