Re: I killed a PC.
I had one brick character die a spectacularly disastrous death. Understanding that nuclear weapons are precision instruments which will not go nuclear if anything sets the explosive off besides the precisely-timed detonators within it, I broke open the case preparatory to removing the uranium core (that character was radiation resistant). The GM, knowing perfectly well that any bomb will explode to maximum effect if hit with any sort of hammer, had the bomb detonate to its full, nuclear effect.
Of course, I knew that everyone else in the room had my specialized knowledge right up to the moment the GM almost gleefully announced: "The Bomb explodes, killing you and thousands of innocents! Write up new characters!" We fired him on the spot. We also habitually stopped and asked pointed questions regarding whether the GM's special knowledge agreed with the player's special knowledge before attempting to destroy anything more complex than an anvil.