Christian Bale stayed in character for lunch meetings with American Psycho writer Bret Easton Ellis, who became so uncomfortable he had to ask the performer — who is known for his method acting — to stop.

The novelist said, “That was in 1998, I think, when that happened. I didn’t have an issue with Christian Bale doing that at the time, it was just seriously unnerving… I was unnerved that I was in a restaurant with someone pretending to be this monster I created. I just wanted him to stop.”

Bale’s dedication to his craft didn’t end there.

During production, he spoke with an American accent at all times — and it was so convincing, that when he spoke with his native British accent at the wrap party, many people on the film’s crew thought that was a fake accent he was perfecting for an upcoming role.

Christian Bale based his performance for Patrick Bateman off of Tom Cruise.

When speaking about the Academy Award winner’s inspiration for the heartless Wall Street killer, the movie’s director, Mary Harron, told BlackBook, “We talked about how Martian-like Patrick Bateman was, how he was looking at the world like somebody from another planet, watching what people did and trying to work out the right way to behave. And then one day, [Bale] called me and he had been watching Tom Cruise on [The Late Show With] David Letterman, and he just had this very intense friendliness with nothing behind the eyes, and he was really taken with this energy.”

During production, Willem Defoe (who played Detective Donald Kimball) was asked to film each scene three different ways: 1. As if Kimball knew Bateman killed Paul Allen (Jared Leto), 2. As if Kimball didn’t know Bateman killed Allen and 3. As if Kimball wasn’t sure if Bateman killed Allen.

The director then edited the takes together, leaving what Kimball thought of Bateman ambiguous to the audience.

Despite being prominently featured in the film, Huey Lewis and the News’ “Hip to Be Square” wasn’t included on the film’s soundtrack.

While it was long speculated (and reported) that the musician opposed the film’s violent themes, he actually opted not to be featured on the flick’s soundtrack because he didn’t want to make his fans purchase an entire album just to own the one song.

The distinctive “Whoosh” sound heard during the film’s infamous business card scene is the slowed-down sound of a sword being drawn from its sheath.

To get into character, Christian Bale actually followed the extensive morning routine that Patrick Bateman does religiously.

The film ran into several issues when it came time to dress Bateman.

Many fashion designers didn’t want to be associated with the killer’s wardrobe. Cerruti allowed Bateman to wear their clothes — but not when he was killing people. Rolex allowed any and all characters except Bateman to wear their watches, while Comme de Garçons refused to authorize the use of one of their bags to carry a corpse (understandably).