A majority of my facepalm moments come from my 4th and currently most successful Fortress, which is in a sort of succession game at present.
The Balded Bears of Onslaught and the Merchants of Roasting.
This 12 year old above/below ground fort suffers greatly from Goblin Ambush's, Snatchers, Food issues, Dwarf stupidity, bizzare unexplainable things, and most of my inexperiance overall. And used to be trolled alot by Raccoons until I managed to whipe them from the face of the map.
But for it, it has become strong. I have a crap ton of Legendary Dwarves, I even have an ungodly strong legendary child dwarf who is the daughter of my one legendary woodcutter.
But onto the facepalming...
Most of the deaths from my Dwarves originally occured due to insanity and suicide as a result.
My original Clerk/Expedition Leader took a fey mood when Balded Bears was still a strictly above ground fort before the great walls were constructed, and since I still thought the land was worthless and didnt know how to frickin dig. He went stark raving mad, but instead of drowning himself after stripping down. He stayed in one spot. By the wagon, and eventually I got the message that he DROWNED. But, he was in AIR. Appearently there was just too much oxygen for him, he had mutated into some Dwarve/Fishman hybrid.
And of course, there was the various Goblin ambush when the great walls had been completed, where they still got in and didnt attack my dwarves. They merely chased an animal out into the swamplands and into the various ponds. Ensuring death for the beast as they went with them. I never did figure out why they would go to all the effort to chase a donkey to its watery death.
Of course, the mere fact that the frequency of the attacks of Goblin ambush's, Snatchers, and invasions of Raccoon's into my fortress had forced me to set my military to activate EVERYONE at once is pretty facepalm worthy in of itself. Imagine, 80+ Dwarves, even improperly equipped ones, barreling down on a bunch of Goblins. Or some Raccoons. I had to do this so often that it was impeding me doing much else, let alone moving underground.
Then of course, there was the great drowning. This was was a multi-Goblin squad ambush. They attacked at two points and I had to activate my military in two different squads. Having gained migrants, I was able to do. But, my Woodcutter and another, whome they tried to ambush, killed one of them, and they ran, and they chased after them. Straight into a pond infront of them...And drowned. Course she chased one of the Goblin's in there too. Meanwhile the others chased after the other squad of Goblins, chased the ones they didnt kill off the map. And on the way back, one by one, walked into a pond and drowned.
It wasnt even a suicide. It was just "Congradulations, we won!, hey, where'd everyone go?, glub! glub! glub!". The mayor, and 10 others, aside from the Woodcuter and her friend. The other two were like "I'LL KILL YOU!, glub! glub! glub!"...I had to revert the save on that one. And I made a point to extend the walls around ALL the nearby Water sources so that cant happen again.
Oh, and now, even after my Fort has been tuned up from my friend playing on it. My Dwarves are so interconnected with each other relationship wise, that if one dies, it threatens to cause a MASSIVE tantrum spiral. Leading to save reversion.
Sometimes the game makes my head hurt.