Christian Bale did not receive an Oscar nomination for portraying Patrick Bateman in American Psycho.
Christian Bale permanently shed his child actor status when he took on the role of Patrick Bateman, who is a far cry from his characters before this film. Patrick Bateman is not meant to be a real person in anyway as he is meant to be the prototypical 80's cutthroat, à la Gordon Gecko, but ramped up to eleven. Gordon Gecko is not exactly the most subtle type of character to begin with so what exactly makes Patrick Bateman so much more extreme? Well he apparently murders people for thing making him a literal cutthroat but actually the more important part is the portrayal of his day to day life with Bateman is the epitome of artificial man obsessed with material possessions and his sexual cravings.
Bateman is not meant to be a real man and Christian Bale does not play him as a real man. Bale performance is a heavily stylized turn where he goes about making a man who seems made of plastic or at least has what's usually inside an action figure, empty space. Everything about Bateman seems to amount to that of nothing. He is only defined by his exercise regiment, his suits, his specific business car, his apartment, his meaningless sexual conquests, the only thing that really separates him in anyway are his murders. Bale decides to go out on a limb with his performance with a the style which is being as fake as possible, only ever sliding from this style in the murder scenes. Every line reading, smile, gesture all are incredibly forced, this performance is, in a word, phony but that's the point.
Bateman is suppose to be an satire of the 80's executive and that is how Bale plays him. I will say a problem does arise from the other performances in the film, aside from Willem Dafoe and Chloë Sevigny, which is they don't know exactly how to play the satire. Bale does not have this problem in the lead role though as he knows to go all the way or not go at all. Where some of the supporting players go in and out of artificiality Bale, making their performances seem off and not in a good way, Bale knows to make this quality the core of Bateman as a character. Bale makes it clear that in the daytime this is exactly who Bateman is, and by taking this approach allows himself to have fun with the material even if this material involves quite a bit of murder and even some cannibalism.
This is not a film about Bateman learning anything about himself, he basically says as much in his final narration. This is about observing his behavior from one event to another simple as that really. What this really means is that Bale has to make Bateman deranged sensibilities entertaining in some way to keep any reason for us to watch as the film does not really try to build much suspense or any other intrigue. This is about observing the psychotic Bateman be Patrick Bateman. Bale succeeds in being entertaining and his almost absurdest approach is the right approach for Patrick Bateman in this film. He has the dark comic edge needed for the part and even in the murders Bale always builds to them in that fake salesman voice.
Bale stays mostly on one note except when he slides to the murderous side of Bateman. Bale actually does this quite well as he slides into the more emotional side of Bateman. He handles the transition in a strangely natural way, but still in the Patrick Bateman manner. These are not the 'real' moments for Bateman though as even these scenes are done simply as Bateman's ultimate fantasy. Bale does not portray them as a real psychopath, but a shallow man's idea of psychopath. Due to this Bale plays him as a psycho killer in a fairly broad way, especially in the scene where he whips out a chain saw and seems almost like the monster from a slasher movie. This take does work, and actually properly alludes to the twist before it happens without being to overt about it.
In the end this is a character and a performance that ends up amounting to nothing, of course that is the point as Patrick Bateman is really just one big nothing. He is not even a realistic nothing and Bale is not what I would refer to as believable in this film either. Bale's performance here would actually be quite terrible in different movie, but with the scope of American Psycho Bale's take was the best possible approach. To attempt to have made a real person out of Bateman most likely would have been futile and the film would have become extremely dour extremely quickly. Bale portrayal of Bateman, which is almost a parody in tone, benefits the film the best by reinforcing Bateman's whole conception at all times, while bringing a darkly humorous edge to the proceedings.