Other mistake: When Riggs and Murtaugh are assigned as new captains, they throw their old badges to the Chief and he catches them in his left hand as he grabs the new badges out of the desk draw with his right. In the next shot where he passes them the new badges, he is not shown to have swapped the badges over, so essentially he passed the old ones back to them.
Lethal Weapon 4 (1998)
1 other mistake - chronological order
Directed by: Richard Donner
Starring: Mel Gibson, Danny Glover, Chris Rock, Jet Li, Rene Russo, Joe Pesci, Kim Chan, Steve Kahan
Revealing mistake: During the big gun battle right before the last fight scene, Riggs is shown driving a forklift, and knocking over some barrels on top of Wah Sing Ku, leader of the Triads. When the forklift does the 180° turn, you can see that it is not Mel Gibson, but an Asian stunt man.
Roger Murtaugh: You ever hear of Ebony Clarke?
Martin Riggs: Yeah, she writes those cheesy sex novels. Why? You boinkin' her?
Roger Murtaugh: No I'm not boinkin' her! Trish is Ebony Clarke!
Martin Riggs: Oh, so you ARE boinkin' her.
Roger Murtaugh: Yeah... Yeah, I'm boinkin' her!
Trivia: As Mel Gibson, Danny Glover and Chris Rock leave the Chinese restaurant (down the stairs), you can see the umbrella handed to Chris Rock hit him in the face.
Question: I wonder, what was the point of having a gunfight with the armored man at the beginning of the film?
Answer: It was put in the film to introduce the concept of Rianne and Lorna being pregnant and to bring in the joke about the news article about Roger, not to mention giving the film an action-heavy opening.