A few gems from my experience
We come upon a 10' x 10' room with some trolls in it. We had found a strange potion a while ago, which the rogue was carrying (a Draught of Fire, maximum safe dosage of 5 swallows)
Rogue: I take five swallows of the potion we found and breath into the room.
(killed the trolls, alright, but it came around and scorched the entire party. He died.)
Facing a dragon that we didn't know was an illusion. Entire party, save for me (the party bard) was swarming the illusion, while I hang back by the entrance. The wizard finally manages to hit it (don't ask me why he decided to try to melee a Dragon, I just don't know), and the illusion dissappears. Guess where the real dragon was...
Me: "[explitive deleted]! I turn and swing at it.
Um... that's all I can think of at the moment...