Interesting, I didn’t even know there was a book. The article you linked mentions the film writers said the book was meant to be ambiguous and they wanted that same angle for the movie. I found it hard to not think Bateman was completely detached from reality by the time he gets to the ATM, though I thought it was at least somewhat believable to that point iirc.
The movie (and book I guess) seems to be told from the perspective of Bateman (he narrates and is in almost every scene) so I thought it seemed up in the air if anything was real or just his imagination. I took from it that he himself definitely cannot tell what is fantasy and reality and you were along for the ride with his perception. His murders and their aftermath were pretty outlandish ie dragging the body bag with a huge blood trail past the doorkeeper, the collection of bodies that all mysteriously vanished overnight, the overdramatic helicopter spotlights into his windows during the meltdown phone call, etc. I think the only realistic murder really was the hobo where he could just leave the guy there. And if some were fake idk why any of them would be real.
I have the image of Bateman being just permanently aloof and fitting the ‘dweeb’ description his lawyer gave while nothing happened but him staring off into the distance daydreaming/hallucinating all of his batshit fantasies or maybe scribbling ferociously into his calendar.
It’s actually pretty funny a lot of times, I didn’t realize it’s supposed to be part black comedy going into it. Definitely an entertaining movie