People keep saying that the film leaves it ambiguous whether Bateman killed everyone or not.
No it doesn't. Both Ellis and Harron have said that every murder happened, or otherwise the book/film's points wouldn't mean anything. The reason the lawyer says he had dinner with Allen is because all the yuppies are so shallow and egotistical that they don't care about each other and fail to recognize each other, often mistaking each other for other colleagues. The reason there's no blood in that one shot of him dragging Allen's corpse is because it's simply an oversight. Furthermore, they have said that the seemingly unrealistic nature of the situations where Bateman kills his victims are pure luck. Example, nobody hearing the chainsaw or running around was just luck. Everyone speculating on this topic fail to understand the film's point at all. The reason Bateman is all scared at the end is because he realizes society doesn't care about anything he's done, and that killing everyone was pointless in the end.
YES, I do indeed realize that it simply being luck doesn't make much sense, but they're the creators, not us. They decide what goes, not us. I'd appreciate it if we introduced a rule prohibiting people from promoting this disproven theory on this website.