Kevin Smith and Bruce Willis did not get along well at all on set. Reports surfaced that Willis disliked Smith's direction, felt he didn't interact enough with the cast, and disagreed with Smith's use of marijuana. Smith has counter-claimed that working with Willis was "soul crushing", stating that Willis often refused to listen to direction, was occasionally combative and was generally unpleasant on and off-set.
After one particularly stressful time working with Bruce Willis, Kevin Smith retired to his trailer and punched three holes in the bathroom wall - holes his assistant later dubbed, "Die Hard One, Die Hard Two, and Die Hard Three."
Kevin Smith credits Tracey Morgan for getting him through the shoot by being funny and good-natured. He said that "He's a f*cking dream. Tracy Morgan, I would lay down in traffic for. Were it not for Tracy, I might have either killed myself, or someone else in the making of Cop Out (2010)."
According to Kevin SmithBruce Willis was often unable to improvise with Tracey Morgan. "He seemed shell-shocked by how fast Tracy could make up dialogue and be funny. Tracy was so fun, and Bruce was like, what is he talking about? He started trying to ad-lib," says Smith, "and he'd look out the window and be like, "Is that Connie Chung out there? I think that's Maury Povich". He's naming these names, and you're like, does he have an old TV Guide under the table? Why is he bringing these names up?"
Kevin Smith thought of Harold Faltermeyer to compose the score, feeling that the film was an homage to the 80s cop comedy genre and needed one of that genre's most prominent composers. Faltermeyer had retired, but was looking to come back and, after seeing a rough cut of the film, signed on.
When Kevin Smith found out the studio was going to lock in the title of the film as "A Couple of Cops" so they could run the trailer behind Sherlock Holmes (2009) Christmas weekend he told a producer, "God that title is going to feel like such a fucking cop out." The producer replied, "We should just call the movie that."
Starting on the first day of filming, Bruce Willis intentionally flubbed his lines and mannerisms in order to waste time during filming. He would often refuse to say his lines. One scene with him and Tracey Morgan in a car was supposed to be the two of them talking. However, Willis decided that his character would be so angry at Morgan that he wouldn't talk to him, so Morgan got more lines that scene.
Kevin Smith had been a fan of Bruce Willis for years prior to working with him. Willis, after acting with Smith on Live Free or Die Hard (2007), told him that he was interested in being in one of his films. Despite all this, it was Warner Bros. that suggested casting Willis as Jimmy Monroe.
On the second day of shooting, Kevin Smith stopped by and told Bruce Willis he was a huge fan. As they were sitting down, a group of people recognized Willis as John McClane. Willis turned to Smith and said, "those are the worst ones." However, Smith and Willis had previously worked together on Live Free Or Die Hard.
During a scene shot in front of a green-screen, Bruce Willis lectured Kevin Smith and his crew on their choice of camera lenses. Willis then lashed out at Smith for not knowing the proper specifications for the camera's lens size.
After Jimmie and Paul take Gabriella to the Mexican restaurant, Jimmie's arm is shown him wearing a bandage when they're inside the car at Paul's house. That was because a scene in which Jimmie is attacked by an assassin at the Mexican restaurant was deleted.
The title is a pun, obliquely referring to being changed from "A Couple of Dicks". That title was itself a pun, with "dick" being 1940s slang for "detective," and was actually spoken by Bruce Willis after the interrogation scene.
"Variety" incorrectly stated that the title had been changed from its original one of "A Couple of Dicks" to "A Couple of Cops." Many news sites concluded that the change was a result of the studio disliking the double-entendre nature of the original title. Kevin Smith's previous film, Zack and Miri Make a Porno (2008), had problems with its title as well. It would be changed because no major network would broadcast it before 9:00 pm.
In response to the critical drubbing the film received, Kevin Smith lashed out at the community of film critics on his Twitter account saying, "Writing a nasty review for Cop Out (2010) is akin to bullying a retarded kid. All you've done is make fun of something that wasn't doing you any harm and wanted only to give some cats some fun laughs." Smith also implied on Twitter that he may charge critics for advance screenings of his films, a service which has typically been provided free; this subsequently ignited a strong response from some critics condemning his stance as "dishonest" and "disingenuous".
Tracy Morgan quotes a line from Jaws (1975), which is one of Kevin Smith's favorite movies. He also quotes a line from the Die Hard films "Yipee kay yay mother f...er", which Bruce Willis states he's never seen. He played John McClane in all the Die Hard films.