The scene in which Annette slaps Sebastian was unscripted. Reese Witherspoon and Ryan Phillippe were so into their scene that she slapped him unexpectedly, and Phillippe's reaction is genuine. He was so into the scene that right after the director said cut, he went behind the set and threw up. The director left the scene in the final cut.
Columbia Pictures wanted Katie Holmes to play Annette, but Roger Kumble didn't think she had enough strength of character for the role. Ryan Phillippe was already signed on as Sebastian when Kumble asked about his girlfriend, Reese Witherspoon. "So, basically, we took Reese out to dinner to get her drunk, and we ended up getting drunk," Kumble revealed in 2014. "And I literally got down on my knees and begged her: 'Please, it'll be 15 days, you'll be great.'" Witherspoon agreed.
Ryan Phillippe recalled that after filming a fight scene with Reese Witherspoon where the two of them viciously insult each other, he felt so emotionally drained that he went outside and threw up after it was over.
For legal reasons, Roger Kumble had to ask all of the actors auditioning for Cecile how old they were, because of a graphic sex scene between the character and Sebastian in the movie. "So we were bringing in all these people," he recalled to Cosmopolitan, "and they were all good, but remember Selma [Blair] came in and I said, 'How old are you?' And she goes [in Cecile's bratty voice] 'How old are you?' And she was so obnoxious and I couldn't get it out of my head."
Despite previous reports, Reese Witherspoon was not pregnant during filming. The movie filmed from 9 June 1998 - 15 July 1998, and Witherspoon had her daughter Ava on 9 September 1999. A full year after filming the movie. She was, however, pregnant, when they did the press tours for the film.
Roger Kumble was inspired by Welcome to the Dollhouse (1995). He felt he had never seen anything like it-"so dark," "fucked up high school." It quickly led him to the thought of doing an update of Dangerous Liaisons, but set in high school.
When Kathryn exits the church at the end of the film a plaque to the left of the doorway says "Rosemond Chapel." Rosemond is the last name of Valmont's aunt in both Cruel Intentions and Dangerous Liaisons (1988).
Production designer Jon Gary Steele, had it so that all of the locations they were permitted to paint were painted in dark colours. "I see the movie as very much a tragedy," Steele said in the film's production notes. "Since we were using a young cast, I didn't want it to feel like a young, bright teen film, because it's not. It's very tragic; everyone basically loses."
Porn star Alisha Klass appeared as a cheerleader, but her brief scene was cut. You can see a glimpse of her in the lower right hand part of the screen when Sebastian is talking to Annette on the phone.
Cruel Intentions (1999) heavily influenced the 2002 story-line in the long-running British soap opera Coronation Street (1960) which Tracy Barlow (Kate Ford) makes a bet with Bev Unwin (Susie Blake) to sleep with Roy Cropper (David Neilson).
The trivia items below may give away important plot points.
One version of Roger Kumble's screenplay had an ending where Annette, instead of publishing the journal and crushing Kathryn, keeps it to herself and announces her cruel intentions to play games on Kathryn under the threat of revealing the contents.
Toward the end of the film when Kathryn tells Ronald that Sebastian had hit her, the actual scene of Sebastian striking her was filmed, but it was deleted because the dialogue from Sebastian during this part didn't fit his character, and the writers decided to let the audience decide for themselves whether he actually did hit Katherine or she made it up.
After her public humiliation, Kathryn Merteuil's cross gets pulled open and her cocaine falls out, referencing the scene in Dangerous Liaisons (1988) in which the similarly disgraced Marquise de Merteuil (Glenn Close) sweeps a cloud of white powder off her dressing table.