Mine was when the deck of my battleship was carpet bombed. Amazingly only one person was affected, but this man, nicknamed disgruntled bob, had the worst death ever. The force of the bombing knocked him into the nuclear generator on board the ship. The bombs also knocked the entire deck off of the ship and the bridge collapsed into the generator as well. The resulting explosion ripped the battleship into pieces, with disgruntled Bob at the heart of it all. When this was done, his little pieces of bite sized carcass drifted to the sea floor where they were devoured by sharks. Needless to say, he died.
I guess the second most painful death ever was when the entire High Ordnance Delivery System's (Rail mounted artillery for launching highly explosive nerve gas shells up to miles away) weapons cache of about 5 high explosive warheads, 5 bio-warfare warheads, 5 nerve gas warheads, 5 napalm filled warheads, and 5 tactical nuclear warheads were hit by a stray bullet. The safety systems had malfunctioned prior to this because of an EMP rocket launched from a soon obliterated RPG launcher. The result of this was basically, GAME OVER. This wasn't a single death though; it was the death of nearly 100 minifigs and the destruction of every piece of armor in our arseal.
"I am Aceman, bringer of quote"