When my fortress just started out with 7 dwarves, my expedition leader got into a scuffle with a wild duck and the duck actually killed him!
It turned out that the victim dwarf was the husband of one of my other dwarves. She went into tantrum and pushed one, then a second, and then a third, dwarf to their death in a murky pool. Oh, and the first and second victim were my miners.
This led her to tantrum more but when she went to shove the fourth victim, the sturdy fella was all like "Oh hell no!" and promptly fatally ripped off the arm of the offender and my fortress was saved!
But that's not it! With only two dwarves left, a gang of three ogres (two of them were ogressess actually), stormed in my as-yet-unconstructed fort, and killed one of my two remaining dwarves. The survivor, who by fate was the one to dispatch the tantrum-ing dwarf, actually managed to kill one ogress and the male ogre. Now a pretty damn-accomplished wrestler, this last dwarf wrestled with Fiona (lulz, the ogress) and in the scuffle managed to finger-nail cut her to death, but with now-fatal wounds to the body: ripped-open chest, no legs, one arm mangled, unconscious head concussion. The second before he died, five migrants just happened to arrive!
I can just imagine the migrant dwarves walking into the fortress and the last dwarf - Goden, or something - saying with his dying breath: "Remember what happened here!".
So yeah, I mass-produced some pretty epic engravings afterwards. This was before I went off to sleep, so, as you can imagine, I felt pretty damn happy to have witnessed this... history!