During his hiatus or whatever he read a lot of books and immersed himself in movies and culture. He must have been aware of the concept of American Psycho, or maybe you're too young nowadays it came out 15 years ago.
But there is a solid resemblance that's for sure. Same obsessiveness in the writing.
The way Patrick tries to strangle Caruthers for being so accomplished, or the way he gets enraged by Paul Allens calling card is spot on.
Bateman stabbed hobos, Elliot splashed couples with takeaway lattes
Certainly would think he was familiar, just never mentioned it is all. I know he liked him some Alpha Dog and Game of Thrones, though. And that it fully dawned on him "Everything is better with some wine in the belly."