If an NPC is innocent or just some generic bystander, I will do everything in my power to keep them alive. Even if it has no impact on the game, I'll go out of my way and reload a save eight times if I have to.
Also (in Morrowind, at least): Any time I kill someone, I strip them nude and place their clothes right beside them before walking away. I find it morbidly funny to think of some crazed guy who would go through all the trouble when they don't plan to do anything else with the body (i.e. no implied necrophilia).
If a boss appears right after a save point, I ALWAYS have to land the first hit. If the boss hits me first, I will automatically reload my game.
If I'm playing against someone in the same room, I tend to yell really loud in a grungy voice at videogames whenever, even though I'm usually not that angry. If I'm playing alone and I keep losing, I talk to videogames in a whimpery voice. "Gak-argabluh- aww c'moo-oo-ooon... Why you gotta be like that? That- that ain't cool, man.... whyyyy..."