Relatively tame, but here's my face palm moments.
I'm a new player, so I've been watching captnduck's tutorials. Dug around for some soil, built a farm plot, and promptly started cursing the dwarfs for refusing to plant anything. After much frustration I quit and do some research, and find out that I was watching the old video *facepalm*
OK, watch the correct tutorial for farming. OK, dig and channel water, I got that. And hey I can designate ramps to be removed, so I don't need to bother with this complicated lever/flood gate thingy. Because, well, channels produce ramps, not slopes. Right? I believe the more experienced players are now laughing at me
So I set everything up for two nice farm rooms, including a drainage area, and tap into the brook running through the map. Wait a moment, then try to remove the slope. Discover that yes, I really did need that flood gate and I now have two 11x11 rooms filled with 7/7 water. *facepalm*
New map, I dig a central staircase down and hit a cavern fairly quick. It's filled with nice mud, and a grazer thingy. Hey, it's a grazer, no worries. A little later I start getting blocked messages, and notice that the silly thing went up to the surface, and is blocking my one tile wide hall leading to the stairs. Try to get a squad setup and fail misserably, so I decide to try and dig around it. Apparent this ticked it off, because I suddenly had a dead miner and woodcutter with their heads ripped off. By a grazing animal. *facepalm*