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.
Factual error: In the scene where Riggs and Murtaugh are in the police car, they intercept a transmission in Afrikaans for the first time in the movie. Except it's definitely not Afrikaans (my home language). I think it's Vlaams or Dutch.
Plot hole: The hitman in the tow truck leans into the rear/left corner of the cab as the surfboard approaches. The board hits the glass at the very top, dead center. Hence, it definitely misses him completely, yet the hitman is killed. Windshields don't break into "shards" (which is another mistake made listed here, and as it can't exist, it can't be the cause of death) and the roof is not damaged. He is the driver, and he stops the truck by braking. There is no vehicle collision. It is clear to all viewers that the makers intended the surfboard to be the cause of death - nobody watching the film thought otherwise.
Character mistake: The sign Riggs holds outside the South African Embassy has a spelling mistake. The sign says "end apartheid now" but the word apartheid is misspelt as "aparthied".
Factual error: Nail guns like the one used as a weapon here can not be fired unless the tip is pressed against a hard surface. It will not fire a nail at someone across any space. The first guy is killed by pressing the gun to his forehead, but the second is hit from several inches away (evidenced by the length of each nail still sticking out of the guy instead of them being fully into his body with only the nail heads showing.
Factual error: The amount of money that leaves the cargo container when Riggs and Murtaugh use the car as a battering ram is nowhere near what was inside considering there were at least 4 or so pallets in front of the car. The car didn't have anywhere near the momentum to drive 'through' the pallets and leave them inside.
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.
Factual error: In the scene where the car blasts out the container, the weight of those stacks of money would make it impossible, for a car parked so close to them, to blast them out the way like it does. There must be around 18 pallets of money stacked up on top of each other, even if they only weighed around 500kg each, that's 9000kg.
Other mistake: When the car blasts out the container, the pallets which the money was on, don't come out with the money.
Revealing mistake: When Leo gets his Subway sandwich, he complains that it's tuna. When he holds it up a dark red lunch meat is visible, like salami.
Continuity mistake: At the end of the film when Murtaugh is holding Riggs, the position of the money keeps changing around them, yet no wind appears to be blowing.
Factual error: Towards the end of the movie, Gibson shoots padlocks with his pistol to break them to get into a truck. Mythbusters has proven this cannot be done with ordinary weapons, or even much more powerful weapons.
Factual error: Diplomatic immunity does not give a foreign diplomat carte blanche to openly and brazenly commit extreme crimes in their host country. Arjen Rudd and his men are known money launderers. Once Riggs begins harassing Rudd at the consulate, Rudd launches a violent campaign against the Los Angeles Police Department, assassinating half a dozen police officers. At the very least, the United States would be well within their rights to expel Rudd from the country and bar his re-entry. There is no way the South African government would oppose prosecution of Rudd given these circumstances, doing so would fracture all diplomatic relations with the United States. It is absurd for Rudd to shoot a cop and smugly proclaim "Diplomatic immunity!" after he has done so because it is not a "get out of jail free" card. If Rudd were expelled, he could face prosecution in his home country.
Suggested correction: Before the federal government would declare a diplomat persona non grata, which would be a serious degradation of the diplomatic relations between two countries), they would first have to do an investigation. The entire movie seems to take place in less than a week. There was probably not enough time, especially since Riggs and Murtaugh are playing things close to the vest and not letting people know what they are doing. As for the "Diplomatic immunity" line, he's just being insulting towards Murtaugh.
While it is true that it's difficult to actually expel a diplomat, the mistake is that Rudd acts as if it is impossible. The movie operates as if diplomatic immunity makes it impossible to arrest a diplomat. And Rudd is doing more than just taunting Roger, he believes right up until the end that he can't be held accountable for his actions, up to and including murdering a cop.
Other mistake: During the "high speed chase," Murtaugh stops the car so that Leo can retrieve Riggs' dropped gun from the side of the road. He picks it up and runs back to the car. Murtaugh says, "Give me that," and takes the gun from Leo. But, Murtaugh, being in the driver's seat, wouldn't be able to reach over the passenger seat and a foot or so outside of the car to grab the gun from Leo. It looks like someone in the passenger's seat just reached out and grabbed it.
Continuity mistake: After leaving the Embassy, when Murtaugh pulls over after Leo says there's a deli, he parks in front of a white car and is near a bush and some grass on the ground. From inside the car, the white car is no longer present and when the door is ripped off, they are now parked in a different spot, no bush or grass is around.
Visible crew/equipment: When Riggs turns up at the house as the pool cleaner you can see the reflection of the camera crew in the window as he walks along the balcony.
Visible crew/equipment: When they fall out of the hotel and into the pool the side shot shows two dark things under the water - this is the under water crew filming the close ups of the actors. The crew cannot be seen in any other scenes around the pool, only on the entry scene.
Audio problem: In the shoot out scene in the stilt house, Riggs is running up the stairs and falls - he has his Beretta in his hand, finger off the trigger, but you can hear it fire three shots. No one else is around or shooting at him, since the bad guys are on the run.
Continuity mistake: After Riggs uses his truck to pull down part of the house on stilts, the tow cable on the back of his truck disappears as he drives away while the house is falling.
