This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Lethal Weapon
Pretty much any scene where Riggs is pissed off at someone or suicidal. Most notably:
In the first movie when he breaks free of his Shock Torture, before going after Joshua.
Earlier on when Murtaugh didn't take his suicidal tendencies seriously until he almost shot himself.
The second movie when he finds out that The Dragon of the group killed his wife.
Then, the moment he escapes from his Death Trap where he was left to drown, he sees his current girlfriend, Rika, already dead next to him in the water. The fact that little bubbles come out of her mouth and nose and her eyes are wide open in terrordoes not help.
The scene where Murtaugh learns that the Shadow Company has kidnapped Rianne. After the failed hit on Riggs, he gets a call from dispatch, claiming that they found a body a couple blocks from his house. When Murtaugh jokes that the victim is probably blonde and has dimples, the dispatcher simply says "How did you know that?"; to reiterate, those Shadow Company bastards killed a ''teenage boy'', Tearjerker whose family will never have Christmas with him again.
Riggs' and Murtaguh's torture by the Shadow Company.