At first glance, the movie may appear very gross and terrifying. However, it somewhat ceases to be when you realize that most of it was probably imagined by Bateman. I mean, some of the situations in the movie are so unbelievable it's hard to believe they could be true. However, the movie is actually a very well written satire of the corpo world.
The movie takes all the stereotypes about businessmen and mocks them in a sophisticated manner. The overt attachment to unimportant details, like business cards. The obsession with always having the most expensive things (Bateman remarks that Allen's flat overlooks the park and is surely more expensive than his). The omnipresent misogyny, depicted in a very grotesque way. The fruitless strife to maintain originality (Bateman bores his visitors to death with detailed information about obscure rock bands).
It may be exaggerated, but i think that the movie paints a surprisingly entertaining vision of many things that are wrong with society.
For instance, Bateman murders first victim Paul Allen, because he can easily get a reservation at an expensive restaurant, while Bateman doesn't seem to be able to no matter what. That drives him to hatred.
Bateman may be the one who "snapped", but it appears obvious that other corporate workers are similarly "corrupted" - it's just that they have grown used to it.