I just had one last night. A dwarf had breached the HFS, so i quickly set him to "masonry" and tried to wall it up. However, a spirit of fire had popped up, and he quickly met a quick, horrid, burning end. Now, the rest of my dwarves were down a LONG 2 tile wide tunnel, so i quickly ordered 2 masons to build a wall down the hallway. Now, i have my ONLY miner mining nearby. So, i try to have the masons save him. However, the Clowns of Fire were too quick, and son roasted one of my masons while the other ran. Fortunatly, another peasant was wandering around, so i drafted him so he could distract the CoF's while he build a wall furhter down. The mason was scared, and went off to get a drink, so he wouldn't do it, but soon, MORE showed up, and it was too late. My dwarves were slaughtered.
2nd facepalm: as the CoF's were destroying EVERYTHING, i notced them approaching an access floodgate that leads to several pipes that feed the waterfalls in my dining room. I watch as one approaches, and soon utterly DESTROYS the floodgate. This leads to MASSIVE flooding through my fortress. Well, it would have, except that the CoF decided that it would stand in front of the approaching water, and began to evaporate it.
3rd facepalm: as the Cof's were destroying everything, i quickly ordered my dwarves to wall themselves in. i considered drafting several of them and having them stay inside safe rooms, but i decided against it. Too much work and all that. Then 3 of them ran out into the hallway JUST as the last wall was finished. >.<