Brings me back to the Golden Globes considering The Martian a comedy.
The way I see it, the overarching writing of American Psycho makes it a satirical/black comedy film, but it does have horror/slasher elements to it, and since it takes itself too seriously, even as a black comedy, I can understand people classifying it as a horror film. I dont really associate it with psychological horror myself tbh. Sometimes the "Psychological" tag in films is a bit loose. Another example is Black Swan, which is also considered psychological horror according to Wikipedia, which I think its weird. At most its a psychological thriller or drama. Certainly the "psychological" part is present, but I dont find horror elements in that film.