Lethal Weapon 4 (1998)

Factual error: Riggs is shown using a laser-sight on his handgun throughout the entire movie. However, almost every single time he turns it on, the entire "beam" of the laser is visible, which doesn't happen in real life unless there is smoke/vapor/debris in the air. Obviously done for the sake of the audience seeing where the laser is pointed, but still a mistake.

Factual error: When the sedan is struck by the train, it launches into the air and explodes, but doesn't sustain severe impact damage. The car rolls over in midair and it is nearly straight - not heavily bent or crushed as the entire left side should have been. Even a slow moving train heavily batters the passenger vehicle it hits. (00:17:05)

Factual error: Early in the film, while Riggs, Roger and Leo are on the Code 7, Riggs has to place his Beretta in his mouth so he can board the larger ship. The Beretta 92FS is a heavy handgun, it would be very difficult, if not impossible, for it to be held in the mouth, let alone to wave your head about like in the film. I own a Beretta 92 and I've tried it, so I'm speaking from experience.