The scene where Carter and Lee are running down the street naked in Hong Kong was an actual take. Production could not block the street off for the shoot.
Don Cheadle (Kung-Fu Kenny) agreed to do this movie only if he got to fight Jackie Chan (Inspector Lee) and speak Chinese.
The counterfeit dollar bills used in the movie say, "In Dog We Trust". During shooting, some extras walked off the set with some of the fake cash, and it eventually ended up in a few casinos in Las Vegas, Nevada. The situation went so out-of-control that production was briefly shut down when the FBI subjected the props department to an investigation to determine whether or not they violated the Counterfeit Deterrence Act of 1992.
In an interview, director Brett Ratner admitted that the first part of the karaoke scene with Chris Tucker was not supposed to be filmed. Tucker refused to act like Michael Jackson with the cameras running. Between takes, he went up as entertainment for everyone. Secretly, Ratner told the cameramen to film it, but to not let Tucker notice them.
At the time of filming, Ziyi Zhang did not speak any English, so she had to take directions via the combination of an interpreter (often Jackie Chan) and director Brett Ratner, who did not speak any Mandarin, performing charades. Her character only says three English words in the movie: "Some apple?" and, later, "Out!" In an interview, Roselyn Sanchez said that Ziyi Zhang tried learning English from her, but tried to discourage her as she would have ended up speaking it with a Puerto Rican accent.