My first tantrum spiral. From something stupid on my part, too.
So I suddenly decide to set up a fortress guard and a prison.. although I set up the guard before the prison even exists. And the 10 guards are all legendary sworddwarves. Whoops.. Apparently I had failed a mandate earlier, or something, so because of the lack of restraints the guard captain decides to issue a beating. With the edge of his sword. He walks up to the dwarf who is happily engraving everything with the other 80 dwarves and cuts him down. Soon one of the nurses starts to have a tantrum, and is called down to the noble rooms by the mayor to have a meeting. She talks to him a bit, runs out the door to start a fist fight, and soon returns to the mayor's room missing both of her arms and bleeding everywhere. Then she crumples in a pitiful heap in front of him.
Now pretty much all of the lowly surfs are throwing tantrums and losing their arms, and I'm too amused to get rid of the guard at this point. The guard captain is running around killing everyone (including guard members), and everyone is running around punching each other and killing puppies. Suddenly I get a message that my mayor has been struck down.. apparently he was sliced open by the guard captain for something or another, and the captain took the mayor position for himself.
To make matters more hilarious, my gigantic hospital was full to the brim with dying people, so I locked the doors and flooded it with my river-filled well. So now I have an insane fortress guard going around slicing everyone's arms off, a bunch of engravers punching everything, and a flooded hospital filled with floating dead bodies. It's like a dwarven fish tank.
Oh, and before all of this I assigned a bunch of mothers to a squad and sent them into the danger room with their babies. Needless to say, all of the babies were impaled in the plated arms of their mothers.