Responding to others;
Compulsive reloading. My favourite instance being Firearms (mod for HL) where they have the magasine system (as opposed to the pool of bullets system), BUT, you can amalgamate your magasines into more full (for example go from 29, 28, 29, 7 to 30, 30, 30, 3), that's a re-loaders wet dream!
Hoarding powerful disposable items throughout an RPG, and maybe using them at the end (elixirs, powerful grenades, shurikens) that kind of thing.
Taking my sweet time on an RTS (every RTS going), last instance was Z: Origins (Z from Win95 RTS) on Android where I would rush getting the flags, and then camp while building up a massive force to take the fort (which easily a smaller force could have achieved).
My own;
Being too nice. This is like the "anti-being a git bad guy", but basically, on an RPG, even if its completely obvious that the nice option is stupid OR I'm being scammed, I will do it anyway (KOTOR games where given a hobo 2000 credits equals those coveted 2 light side points, when I'm already at 100% lightside...)
Quick Save/Quick Load. Always having to 100% win at an RPG minigame (pazaak), always having to do that Max Payne dive perfectly, annoyed at HL when a headcrab took my health down from perfect 100/100.
Starting a game when I know I actually want to play a different game... I did this for Mass Effect 1 when I wanted to play Fallout 3, and then didn't return to Mass Effect for a LONG time. Got 50% the way through GTAIV, because I wanted to play Bioshock.
Replaying old games when I have a new game I should really complete. "Oh I'm 75% the way through borderlands, let me check out this Mechwarrior Online trailer... looks ok... not as good as MechWarrior 4, hmmm I should really play MechWarrior 4". A joystick and 10 hours later and I've completely forgot about borderlands...