i dont pay attention enough to name a particular dwarf for their stupidity, but i think my fort as a whole deserves this award on several occasions.
To name a couple of extreme derpwarf moments one was when i was being sieged by undead and attacked by a forgotten beast, this was one of my older forts where the locks were raising bridges instead of hatches and my dwarf refused to pull the lever on either and let both in... gg
another time, more recently is i ordered my dwarves to pull a lever linked to my aquifier hatch twice so it opens and then closes immediately, and most of the time they do it without leaving the lever but this time some derpwarf left without pulling the lever a second time so my hospital's water zone ended up being flooded with water from the aquifier since i just needed 1 drop of water to refill the one 6/7 water tile. I ended up having to remove the doors to the water room to let the water out while trying to get 1 derpwarf to pull the lever to stop it. That went very smoothly as dwarfs refused to move in the water tiles 4/7 deeper or more, and alot of them got stuck.
When it was finally over they refused to clean up the muddy masterwork engraved floors, causing plants to grow on it and the masterwork engravings to be ruined. This not only caused my legendary engraver to tantrum but also made it so that if the plants were removed the tile reverted to soil, meaning it could never be engraved again. Note: my hospital and hospital water reservoir are connected to my legendary masterwork engraved dining room in my design so that food and water can easily be brought to patients in the hospital.