When Patrick drags Allen's body along, blood spoils from the bag. When outside, there's no blood anywhere.
Patrick's CD player in his apartment is missing in some scenes.
(at around 28 mins) When Patrick Bateman murders Paul Allen, the collar on his raincoat changes from being folded on both sides, to one side raised, to half the collar up back to folded on both sides. This alternates between many shots.
(possibly deliberate errors by the filmmakers): In one of the last scenes where Patrick enters a bar/restaurant, a door to his left has a sign on it saying 'NO EXIT'. However, in the last scene where Patrick is sat down and takes a drink from his glass the door behind him now reads 'THIS IS NOT AN EXIT'.
(at around 24 mins) Bateman is at the Christmas party wearing reindeer antlers. As the camera shot changes from front to rear, the antlers move from behind Bateman's ear to in front of it.
At around 1hr 2min Patrick holds a nail gun to the back of Jean's head while they are in his apartment. The nail gun shown is a pneumatic air nail gun that would need to be connected to an air compressor with an air hose to function. The only way he'd be able to kill Jean with that nail gun would be to bash her over the head with it.
Early in the film, Bateman and his fiancé take a fictional route to Espace. The restaurant was located on East 16th Street, between Fifth Avenue & Broadway, but the cab is shown driving through Chinatown (downtown Manhattan, below the numbered streets) and under an elevated train to get there. There are no elevated trains in lower Manhattan, only north of Central Park.
Bateman's bullet clearly hits the police car at the trunk, in the rear when it blows up. There's nothing flammable in a car there in the first place, but a pistol bullet also wouldn't blow up a car, not even if it hits the gas tank. After the explosion the cop who stood behind the car simply vanishes. If he was caught in the fireball, he'd be running around on fire.
(at around 31 mins) When Bateman leaves the message on Paul Allen's voicemail, he ends it saying "hasta la vista, baby", Bateman was quoting the ending of "Looking for a New Love" which is a song by American dance-pop singer Jody Watley. It was released in January 1987 and reached number two on the US Billboard Hot 100 in May 1987 and spent four weeks at number-one on the US Billboard R&B chart. Bateman was not quoting Arnold Schwarzenegger's catchphrase from Kẻ Hủy Diệt 2: Ngày Phán Xét (1991), which was released in 1991.
(at around 43 mins) While rhapsodising about Genesis' "Invisible Touch" LP, Bateman states that "Phil Collins addresses the problems of abusive political authority" on the song "Land Of Confusion." That song's lyrics were written by the band's guitarist/bassist, Mike Rutherford. But all of the songwriting credits on that Genesis album were indiscriminately credited to all three Genesis band members (Tony Banks, Collins, Rutherford), so Patrick wouldn't necessarily know who wrote the lyrics to which specific songs.
'Acquisitions' is spelled incorrectly (as "aquisitions") on all the business cards.
(at around 9 mins) Patrick pronounces "Robert Palmer" as "Robert Parmer", revealing a flaw in Christian Bale's staged American accent.
All of the windows show views of the cityscape with the horizontal line far above normal. This signals that the views are backdrops which are set too high. Often one looks up at a character and at the same time looks down on the streets, which is impossible.
When Bateman goes to Paul Allen's apartment after killing him, he points out he used the keys he had taken from Allen and notices that Allen's apartment "overlooks the park"...virtually all buildings that overlook Central Park in Manhattan have doormen, and it would have been almost impossible to get in without having been witnessed, or having to sign in, and identify himself.
When Jean is going through Patrick's notebook at the end of the movie, the calendar is off. For example, in 1987, November 20th was on a Friday, whereas the calendar said it was a Saturday.
The telephone next to Patrick Bateman's bed is a Bang & Olufsen model not available in the 1980s
(at around 1h 30 mins) The TV that is shown at the end of the movie with President Reagan speaking is a late '90s model of Sony Trinitron.
(at around 1h 28 mins) When Bateman is using the pay phone on Park Avenue, the skyscraper in the background says "MetLife", when it should say "Pan Am". Although the building was sold by Pan Am to Met Life in the 1980s, the name displayed on the building wasn't changed until the early 1990s.
(at around 9 mins) Early in the movie, Bateman comments that he is listening to the new Robert Palmer album. The song that's heard during this scene is "Simply Irresistible", which was on his album Heavy Nova, which came out in November 1988. But the Ronald Reagan speech seen at the end of the movie occurred in early 1987, not 1988.
(at around 14 mins) The porno movie that goes on during Patrick's telephone conversation with his fiancé is taken from Red Vibe Diaries: Object of Desire (1997), produced in 1997.
(at around 1h 4 mins) As Jean is leaving Patrick's apartment, she reminds Patrick of his lunch appointment the following day, but the second-half of Jean's line appears to have been dubbed. It is unclear what the actress was actually saying.
(at around 37 mins) When Patrick Bateman is "watching" Tử Thần Vùng Texas (1974) (while exercising) the screams of Sally Hardesty are inconsistent with the original soundtrack.
(at around 12 mins) When Bateman is at the ATM getting cash out, the lady walks by him. As he walks to catch up to her, the camera and crew are reflected in the glass of the storefront windows.
(at around 1 min) Camera and mount are briefly visible in the first shot of the title sequence, reflected in the silver knife (albeit distorted).
In multiple scenes at Bateman's apartment, the crew and camera operators are visible in the reflection of his bedroom TV.
(at around 1h 21 mins) During Patrick's killing spree towards the end of the movie, when he is running between the two nearly-identical buildings, a Canadian flag is intermittently visible flapping out from behind the building on the left, revealing that this scene was shot in the Toronto-Dominion Plaza, not in New York.
Bateman's office is supposed to be located downtown, yet the view out his window is clearly of midtown.
At his apartment Jean asks Patrick if he's seeing anyone. It is odd that his secretary would know nothing about Patrick being engaged.
(at around 52 mins) When Bateman is with Courtney at her apartment and gets off the bed to dress up, the mic can be seen on the mirror of the bedroom.
(at around 51 mins) During Detective Kimball's second interview with Bateman, the reflection of the microphone can be seen on the CD to Bateman's right.
(at around 47 mins) Patrick attributes the quote, "When I see a pretty girl walking down the street, I think two things. One part wants me to take her out, talk to her, be real nice and sweet and treat her right. The other part just thinks what her head would look like on a stick", to Ed Gein. However, it was actually Ed Kemper.
(at around 41 mins) The album Bateman holds up while entertaining the escorts is Phil Collins' solo album "No Jacket Required", although "In Too Deep" is from the Genesis album "Invisible Touch". Although it seems like a minor error, someone as obsessed with pop music as Bateman is would be unlikely to make such a mistake.
(at around 1h 12 mins) Whitney Houston's 1985 debut album entitled "Whitney Houston", contains three number one singles, not four as stated by Patrick when Christie and Elizabeth are making out. Whitney Houston's second album entitled "Whitney", contains four number one singles and was released in 1987.
(at around 27 mins) Patrick Bateman stated that the Huey Lewis & The News album "Fore!" was released in 1987 when it actually was released in early 1986 as a follow up to their single "The Power of Love".
(at around 4 mins) When Patrick tries to order drinks at the Tunnel bar, he asks for "two Stoli on the rocks." Instead, he receives two Stoli's up (no ice).