Had a game i was doing pretty well on, was turning away a few minor attacks and looting the corpses. Then get one particular attack of 8 goblins, kill 6 of the 8 goblins easy, then the last two went and slaughtered 30-40 dwarfs before a peasant eventually put him out his misery, i then find a fortress which can't cook cos the cooks died and everything is rotting.
Trading... no more is needed i suspect. I begun trading thinking the stupid negotiation thing was it, i was like wuttef is this? where's my stuff i ordered? still don't understand that negotiation thing, ah well, maybe another time. Started trading properly and just bought iron mostly, as i've not actually found any iron ore yet, closest i've come is tetrahedrite. Then i realised you just literally sold a few wooden iron balls and some roasts and you can take the whole caravan, very useful seeing my current area has very little wood and lazy dwarfs too lazy to cut it for some reason.
Waiting 20 minutes for my trader to go to the trade depot, to realise my trader isn't my broker. Surely everyones had that one?
Started a new map, started getting some cool fortifications together and doing pretty well spending a good few hours on it, then to realise that the entire third level is flooded and i have no form of rock WHATSOEVER, no way to build pumps and no clue of how to fix the problem.
Finding an area with a necromancer on it when i suck. So got "boned" by skeletons, didn't do too badly, but heck was too much of a pain in the arse to deal with for too little reward.
couple more from my current fortress:
annoying the dwarf caravan cos i'd knocked out my expidition leader and had not leaders, so they sat by him for ~5 months before i changed expedition leader, then they got pissed off and left. Slightly amusingly, he got knocked out making the well which was then used to give him water.
Had a fairly useful woodcrafter in my military, who chased a kea or something into a river and forgot they he couldn't swim, so i lost him. Took me ages to get the bugger out too! had enough of ghosts in my last game.
From a previous fortress, killed ALL my miners by digging so deep they were too far away from food to go back for it and died in the pit they were in, either that or i made them lose their wills to live. I sent some more dwarves to bury them somewhere, they got lazy and couldn't be assed to come back up, except one looked at the corpses and thought "not for me" and ran off back up the stairs. Left 6 dead dwarfs to haunt my fortress (which then got killed by above mentioned 8 man goblin siege)