Other mistake: Several close-ups of the business cards of Patrick Bateman and his associates reveal a misspelling of the word "Acquisitions" (the "c" is missing - not a small error, given that this is the name of their department).
Visible crew/equipment: In the scene after Patrick Bateman's second encounter with the detective in his office, we see Bateman having sex at Courtney's apartment. After he rolls off her, Bateman approaches the large, stand-up mirror in the bedroom. In the upper right hand corner of the mirror, a boom microphone can clearly be seen moving around to pick up Christian Bale's lines. The next time we get the same long shot, the microphone is gone.
Continuity mistake: In the scene where Patrick is in his office working on a crossword puzzle before talking to Jean, he is writing with his right hand. When the shot changes to the reflection of Patrick's glasses, the reflection shown is as if he is using his left hand. The reflection isn't a mirror image as it should be.
Character mistake: Patrick, being the music buff that he is, mistakenly claims that Huey Lewis' Fore! came out in 1987, when it was actually released in 1986.
Continuity mistake: In the office scene where Paul Allen walks up to Patrick Bateman and mistakes him for Marcus, Paul crosses his arms as he starts talking to Bateman. The angle changes and his arms are suddenly straight.
Continuity mistake: When the detective is in Patrick's office questioning him about Paul Allen's disappearance, there is a bottle and a glass on the table. A glass ashtray appears by the bottle and the glass then disappears between shots.
Revealing mistake: In the scene where Bateman is in the shootout with the police, there is a shot looking over the left shoulder of the policeman at Bateman. While they are shooting, the gun is visibly out of bullets because the slide is locked back, however it keeps shooting anyway.
Continuity mistake: When Bateman goes crazy and flees into his office, his hair is very messed up. However just after he sings and goes to his office, it is quite obvious his hair has been redone and gelled again.
Visible crew/equipment: In the scene where Patrick Bateman is walking the streets, just before that encounter with the lady who is waiting for the red light to change, you can see the camera crew reflected on the store windows.
Factual error: When Bateman is in his apartment with his secretary, he points a large tool at the back of her head, unbeknownst to her. That is an air powered nailgun for installing plywood. The only way that one could be used is with an airhose and a compressor. The fitting for the airhose that sticks out of the bottom has been removed because it usually would point straight down and stick out about 2 inches.
Other mistake: In the scene where Bateman is about to murder Paul Allen, he turns on the CD player and walks towards the axe meaning to say "...song's so catchy;" but if you watch his mouth, you can see that in place of the word "catchy" there is a blatant voiceover. Who knows what he said in the original shooting.