Continuity mistake: Near the end of the car chase you see a shot of the station wagon Riggs and Murtaugh are riding in get held up by a couple of police cars. The hood is popped open. The shot changes to the BMW crashing into the store window and then back to the station wagon. The hood is down.
Continuity mistake: When the bathroom explodes, from one angle we see the toilet come sailing out over the roof of a police truck parked at the front of the house. While the angles make it a bit tricky to judge, there's a definite leftward trajectory. We then cut to a closeup of Murtaugh's car, and the toilet lands on it as if it was flying to the right. Even if the angles are misleading, in the first shot the police truck and other cars are parked to the right of the exploding window. In the shot of Roger's car he's also parked to the right, but without all the cars visible around it which there should be.
Continuity mistake: In the scene where Riggs and Rika are in the trailer while the men in the helicopters are shooting, after the scene where you see the T.V. fall down, You see the cabinet being shot. If you look carefully, you can see pieces of the cabinet fall down, then appear again. Director's cut.
Continuity mistake: When Hans first walks into the room with the fishtank, the plastic on the floor flaps up behind him as he walks, ending up folded up on itself without much space between the man and the end of the plastic. When he gets shot and falls back onto it, it's perfectly flat and he's a lot further forward.
Continuity mistake: In the scene where Murtaugh is shooting his attackers with the nail gun the walls are apparently covered with super plastic. How is it that the plastic sheeting is light enough for the bad guy to punch through, but is able to support the weight of his corpse by a single nail when Murtaugh shoots him through the plastic? Wouldn't the plastic tear and drop the body to the floor?
Continuity mistake: In Lethal Weapon 1 Murtaugh turns 50. In Lethal Weapon 2, you can see a copy of Murtaugh's police file in the South African Embassy, when they are discussing repercussions against the police. In the file it says Murtaugh was born in 1947 which would make him 42 in this movie.
Continuity mistake: Near the end, when Riggs is captured by the bad guys they tie him in a straight-jacket and toss him off a pier into the drink, he's wearing a pair of Dingo style boots. Underwater when he dislocates his shoulder and escapes the straight-jacket, he sees Patsy Kendit's corpse, swims over, checks her pulse and swims to the surface. Now he's barefoot. Yet when he attacks and kills the two thugs he's got the boots on again. They can even be heard on the pavement.
Continuity mistake: During a chase scene involving Murtaugh's station wagon and a flatbed tow truck, the hotel waiter shoots at Riggs through the truck's rear window. In this series of shots, notice how Riggs is swinging by a chrome handle on the passenger's side - which wasn't there during the gunpoint hijack shot just moments ago.
Continuity mistake: After Murtaugh confirms the Alba Varden is a ship, one of Rudd's henchmen enters the house armed with a knife. Moments later when they're struggling by the hobby room's blueprint table, Murtaugh grabs the nail gun and shoots him in the forehead. Now right here, you can notice the sound of a knife being thrown to the floor as he reaches for his head. But when the henchman is up against the unhinged doors, he's once again holding a knife in his right hand.
Continuity mistake: When Captain Murphy is briefing Riggs and Murtaugh on their Leo Getz assignment, a small red No Smoking sign can be seen facing outwards on the desk. But as Riggs and Murtaugh stand up to leave, notice how the sign has momentarily turned itself around to face the Captain.