Mid-Development Genre Shift: Ellis originally imagined Bateman as a disillusioned but nonviolent protagonist. After a dinner with friends who worked on Wall Street, he decided to make him a serial killer.
Shrug of God: Ellis stated that even he doesn't know whether Patrick is a real serial killer or not.
Technology Marches On: Patrick's state-of-the-art home entertainment toys seem a bit quaint when read now.
Write Who You Know: Ellis has described Bateman as being based on his father. His idolization of Donald Trump was based on his friends' respect for and envy of the mogul.
Actor-Shared Background: Patrick once justifies his assumption that Elizabeth is a lesbian by reminding her that she went to Sarah Lawrence. Guinevere Turner (who plays Elizabeth) is a lesbian, and really did go to Sarah Lawrence.
Fake American: Christian Bale, a Wel-English actor, played Patrick Bateman in the film. He spoke in an American accent at all times, and was so convincing and thorough with it that when he spoke in his normal English accent at the film's wrap party, everyone was surprised since they genuinely thought he was American.
Method Acting: Bale took quite some extremes to invest himself into the character of Bateman. Besides the examples listed above in Dyeing for Your Art and Fake American, Bale also extensively studied the novel, distanced himself from others on set (as Bateman would have), and actually maintained the famous morning routine described at the start of the film.
Star-Making Role: Despite being warned that playing Patrick Bateman would be "career suicide", the film wound up garnering more attention for Christian Bale, with the success of the movie and his performance landing him bigger leading roles, eventually leading him to play Batman.
Throw It In!: There are two scenes that involved improvisation by Bale that was kept in the movie: the jump-rope scene (Bale crossing his arms was improvised) and the Moonwalk Dance Bateman does, so as to hide his axe, shortly before killing Paul Allen (which was one of the only problems the author of the original novel had with the movie).
At least three screenplays were written: one by Matthew Markwalder, one by Mary Harron and Guinevere Turner, and one by Bret Easton Ellis himself. Harron and Turner's script is what ended up in production.
After the novel was originally optioned in 1991, Ellis himself was set to write the script for director Stuart Gordon with Johnny Depp starring as Patrick Bateman. Gordon wanted to do the film in black and white and stick as close to the book as possible, meaning a guaranteed X-rating. After the project fell through, David Cronenberg replaced Gordon, with Brad Pitt set to star. This project also failed to get off the ground.
Cronenberg's version of the screenplay had Patrick Bateman in a musical finale on top of the World Trade Center.
Font Anachronism: The business card scene and song number includes a reference to Constantia and Comic Sans, which were released in 2006 and 1994 respectively, while the musical takes place in the late 1980s.