The party was adventuring through the 1st Ed. D&D module, The Temple of Elemental Evil. It is, indeed, a difficult and deadly adventure.
At one point, though, the party was resting in a comparatively safe area, an underground orchard, with trees having different colored fruit on their branches.
A few party members tasted the fruit of various colors. Some fruit restored health, some increased stats, and some granted other abilities. But Reyn Swift, elven archer, decided to try the black apples.
The group cautioned him, saying that black fruit was never a good choice. But he persisted, and bit the apple.
He immediately took about half his hit points in damage; total system shock.
When he recovered, standing upright again, he wanted to try another bite. The party was incredulous, warning him to be sane and put the apple down. But he was, for some reason, convinced that biting the black fruit a second time would yield some beneficial result.
Instead, as per the module, he was magically disintegrated, his body blown to dust in a small explosion, with no chance of resurrection.