The book opens with Bateman on his way to dinner at his girlfriend Evelyn's house. Ellis gives the reader an immediate introduction to the minute attention to detail inherent in Bateman, while also showing how he ignores other details to avoid having human connection to people and events. For instance, he details the clothes worn by Evelyn and her friend Courtney down to the designer, but fails to comprehend the clear signs that Evelyn is sleeping with his friend Tim Price. In Bateman's world, no person is worthy of consideration as a human. They can be envied (like Paul Owen with the mysteriously important Fisher account), desired (as in hardbodies, but not for themselves of course), or derided (most notably the homeless, but also anyone unfashionable), but rarely does Bateman consider anyone else as a wholly formed human.
To be fair, it doesn't seem that many of the other characters consider Bateman as a fellow human either. No one hears what anyone else says, or seems to have authentic human interactions. The exception is Bateman's secretary, Jean, who Bateman only considers as a passably attractive woman who is "obsessed" with him, but who genuinely cares about Bateman (or at least, the Bateman he shows to the world). Jean complicates Bateman's life. He finds himself wanting to confess to her, most likely due to the fact that she is the only person in his life who seems equipped to listen. His girlfriend Evelyn, despite conducting a glaringly apparent affair with his friend Price, decides during the course of the book that they should get married. Her reasoning is that everyone else is getting married. For Evelyn, for Patrick, the individual doesn't matter.
Identity is a major theme of the book. Characters are constantly mistaken for other characters. A person who both Patrick and the reader know can not be in London is seen there, having dinner. Bateman makes dinner dates with people as Marcus Halberstram without any question. Everything is centered on appearance. And this is where the humor shines. There are many moments that would be uncomfortable-- being mistaken for someone else, using the wrong name-- that instead are simple ignored. Bateman's conversations with his friends, while at times incredibly banal and sadly realistic, are also darkly hilarious. The way they don't listen, the way they view the world.
Unfortunately the extreme violence detracts from the humor and social commentary. In 1991, this sort of depiction of violence was revolutionary and revolting. Sadly, it's now an industry. At least one movie comes out every year that is essentially violence pornography. Given the current social climate, it's actually surprising that the movie version of the book didn't feature the same extreme violence. While the violent scenes are technically well-written (the reader remains grounded in time and space from beginning until bitter, bloody end), they do overshadow the broader themes. American Psycho wouldn't have gained the same notoriety without them, but it also most probably wouldn't be derided as misogynist porn.