The dwarven mom that decided to give birth into the hole under my magma forge.
Wouldn't qualify - there have to be no innocent bystanders. Eh, who cares. Mine has loads.
Anyway, how about this one? I got bored of a fortress, and decided to flood the whole thing. The water went down, and before long all my dwarves were stuck inside by the fast flow of water. The dining room was taken out, but brave dwarfs were able to take food downstairs (and obviously water wasn't a problem). Of course, the ones trapped in their rooms (including the count, the tax collecter (who shared a room) and a liason (who was meeting the count)) died quite quickly, so the upper floor became a tantrumming hellhole. One of my gemcutters decided that he'd had enough. He tantrummed, and killed a dog. His own dog, as it turned out. Not only was he arrested (100 days in prison for murder) but he was also furious for having lost a pet. He killed the first guard who came to arrest him, and smashed several buildings. He was eventually taken into jail, where he killed his jail mate, seriously wounded a guard, and smashed his own chain. By this time, he had over 4 years in jail to deal with. The hammerer then decided that enough was enough. He had been trapped outside, and decided to run into the fort. Poor guy forgot that a rather high pressure jet of water was still firing in through the front enterance. He was swept downstairs and fell down the garbage shaft. The garbage shaft was not designed for killing, so the hammerer had to lie at the bottem, seriously injured, as water and random stuff from the fort continued to build up on him.
Then another thing happened. Another dwarf tried to win an award. The rogue gem cutter decided to punch another guard in the head, and seriously injured him. So a clothier comes rushing to his aid. He decides to take the guard to his bed. In the barracks. Upstairs.
Now, I had actually tapped the river in two places. One near the entrance, one in the barracks. However, the door remained closed, so the barracks was now full of 7/7 water. What did the clothier do? He opened the door, sand swum right in. Even as both he and his injured comrade began to drown, he continued to try and swim to a bed. Suddenly, he realises that deep water = bad. He runs a bit, and drops the guard.
Where does he drop him? On top of the door. The water rushed out and swept mr Clothier into the main stream, so he joined the hammerer at the bottem of the garbage chute.