Three stories here. Only one is mine.
Me: I played three hours into a PS1 game on my PS2 before realizing I needed a PS1 memory card to save, and died shortly afterwards.
My boyfriend (the half dragon mindflayer): While fighting the first Hydra in God of War, the circle button appeared over the bosses head. Most people would hit circle to initiate the finishing move, but not him. He attacked the circle relentlessly in an attempt to make it "stop healing the boss".
But the winner is...
My best friend: In a game of Halo, there were five other people on his team. He acidenatally stuck a plasma to one. While trying to get away before they realized it was him, he hijacked a wraith and ran over the driver. It was also his teammate. Embaressed, he hit the thrust, but he was on a hill and couldn't see the other side. Two more teammates became roadkill. This has all happened in about four seconds, so no one had respawned yet. Pissed, he fires a random mortar across the battlefield. Without being able to see, let alone aim, he managed to hit and kill his last teammate. Needless to say, he was booted.