I kinda wanted to leave fortress mode for a bit, but rather than just abandoning it I figured, hey, a tantrum spiral could be fun. I had no military, so I figured letting in a goblin ambush ought to do the trick one way or another... but although the goblin macemen depopulated my fortress from 60 to 12 dwarves, only one became unhappy enough to get an announcement, and he snapped out of it near instantly. I also had two possessed dwarves that didn't have the resources to finish their artifacts, and although they went insane, this also did not affect the overall joy of my fortress. In fact, of the 12 remaining dwarves, only one was particularity unhappy, while walking over the miasma-covered corpses of his fellows and about fifty pets... oh yeah... and being periodically chased by goblin macemen, who where still running around and killing anything they could catch up to (I guess the surviving dwarves where all good runners). In fact, after a while, most of the dwarves decided to get on with their blissful lives, returning to their jobs in between being chased by goblins or elkbirds*. I guess what I'm getting at... the only nice thing I had for my dwarves was a good dining hall (if by this point a bit blood, corpse, and miasma soaked). Does that alone make a big enough difference to permanently overpower any degree of unhappy thought?
Because I had to give up when I literally could not think of a way to make my dwarves any unhappier.
*The elk birds where either harmless or non-hostile. I wish my dwarves would have just ignored them entirely.