Got another...
Ok, the game for this one was Vampire.
The player characters had just murdered the prince of the vampires and were fleeing the city, the prince's henchmen hot in pursuit. (Well, two of them were fleeing, anyway - the third was still working on becoming the new prince. He was a setite and the other two were anarchs, IIRC.)
In a dark park in the suburbs, they suddenly hear a noise of movement.
One of them, the "tough guy" of the group, decides to fast-draw his desert eagle and try to shoot whoever might be there.
He botched the fast-draw check, the gun went off, hit him, and he rolled so much damage that he killed himself. (Technically, he of course was only in torpor but the other PC wasn't strong enough to carry him, nor could she stay enough to hide him. So the sun probably got him in the end.)
By the way, the noise they had heard was a homeless person...