One of my dwarves (a cheese maker, I believe, that I was grooming for a military position) turned out to be a necromancer, of all bloody things. Who knew? I mean, hell, I figured I'd occasionally have to deal with a vampire at best. Well, anyway, trade caravan showed up and filled him fulla arrows when he tried to start shit. Hit him so many times, his body was propelled into my moat. If it ended here, I'd have no problem. But, since he was still technically a member of my fortress, things started getting silly. Then annoyingly silly. Then hilariously silly.
See, since I couldn't get into the moat to fetch his corpse for burial, his evil necromancer ghost came back in a little bit of a bad mood. Kept bringing back his old corpse under the water. This was more or less harmless since the poor zombie was trapped down there - me having pre-emptively removed all but two of the ramps leading out of it and those two impossible to access - and the necro-ghost seemed rather obsessed with hanging out with its bloated zombie corpse, scaring the Armok out of any fisherdwarves that passed by on their way to work. Eventually the corpse would 'drown' (I know, right?) and the ghost would bring it back. This cycle continued for quite some time.
Until the corpse was reduced to nothing more than a decayed skeleton. Then the necro-ghost got fuckin' serious, in the most amusing way possible. He went to the fishery (which had been actively working for half a decade, bringing in mussels) and brought back as many mussel shells as he possibly could, numbering into the hundreds. These ZOMBIE MUSSEL SHELLS then went on a total rampage throughout my fortress (fishery was built inside the walls of my fort), slaughtering every single living thing they encountered, including my 10 expert-level militia-men equipped in steel plate and similar weapons, and 40 other dwarves enlisted as wrestlers. My fort laid low by a single-minded mass of undead crustaceans and their necro-ghost master who guides them from my moat.
Honestly, not even mad. How can I possibly get mad at such an amazingly insane defeat?