Strangest death I've ever seen: Suicide... by fish.
Jack the 12th level Assassin was a hard man. He was doing an aquatic adventure in a merfolk realm. Actually, a merman realm... this was back in the days of 1E/2E, where we didn't have "-folk". Just "-men", baby. Mermen, lizardmen, mongrelmen. Men these days must be a kinder, gentler breed. Just ordinary folk.
Anyway, Jack had a nasty habit of sneaking up behind people and stabbing them. The first victim in this module was a merfolk guard. Very pleased with himself, Jack looted the body. He found only a few fish. One of these was quite large, though. About the size of a french loaf (long, thin bread). Chuckling to himself, he decided to take it. "There's good eating on that!"
Now, what Jack didn't know was that the fish was actually a special breed used by the merfolk as living weapons. They had air bladders in the center which, when squeezed, could propel a small, thin object out of the fish at very high velocities. Usually a poisoned bone dart. I'm pretty sure this came from an old Basic/Expert accessory (PC 3 - Sea People). Of course, Jack had no idea. He killed the guard before he could even draw his "living weapon".
The adventure came off the rails about an hour later. Jack and co had riled up the merfolk, who had them pinned down in a small plaza. Things were looking grim until Jack came up with a brilliant plan. He'd intimidate the merfolk by showing them he was a total bad-a$$... by biting the head off a fish. In the player's defense, he'd recently seen A Fish Called Wanda, and was influenced by one of the characters therein.
So, Jack... the slayer of princes and demons... pulls out his fish, sticks the head of it as far into his mouth as he can, and takes a big bite. Which compresses the air bladder. Which... well, you can guess the rest. I was in tears, clutching my sides. The player just sat there, for a full minute. Shaking slightly. He has since recovered, and Jack's death has now become one of his favorite stories. But it was quite the shock at the time.
"See? I told you I was hard-core..."