Health must always be a multiple of the max
Reload after every shot unless I'm in the process of fighting.
If I have control over it, an odd number of bullets should be fired.
Everything I make has to be symmetrical in Minecraft.
In any RTS game, my army MUST be on the key "three".
In Minecraft, I have to break an odd number of blocks or I get a nagging feeling.
I have a lot more, but that's enough for now.
EDIT: more:
Sounds must eventually play in both ears if I can help it, if it's in the left ear for 5 seconds, I'll turn and let it play in the right ear for 5 seconds, and then try to center it. This normally happens with longer sound files though, as opposed to a quick gunshot or death sound.
Subtitles must ALWAYS be on. Even if I can hear perfectly, they must be on or I can't play they game and enjoy it.
In Blockland, my active paint color must always be a primary color
If I walk over a health kit or ammo kit and don't pick it up, I damage myself or fire a bullet to pick it up.