Reloading when I've got plenty of ammo. I only do it for preparation of fights I think will last longer and thus need more ammo stored in the clip.

Moving while spell casting in WoW. I do this without even knowing sometimes, usually because I keep thinking that the mob or boss is moving out of my casting range when they really aren't, this effectively hurts my spell rotation in the process.

Playing a game for a while, jump out of it for a few months, hop back in again and then out. sometimes this ends up going that way until it's completed, sometimes years later when I feel like coming back to it.

I like to reload a lot. Even if I shot only a few bullets in the middle of combat.

I'm in this situation with Xeno X right now.  

Rage. It's my only bad habit.

I pick up everything that can be sold or has any value at all. I always end up with my storage stuffed if there is a limit or it becomes a bloody massive stockpile if it's unlimited and I have to scroll for days to get to the end.

I don't use potions unless there is no choice. Ended up with over 1000 stimpaks in Fallout 4, for instance. I start out afraid I might not have them when I need them but that just becomes silly after awhile.

I do the compulsive reloading, too. Recently found a gun that gets stronger as the clip empties but I just put it in storage because it's useless for me.

Bethesda games have made me a compulsive game saver, too, but I consider that justified.

I sneak ALL THE TIME. Even around friendlies. I was in an allied stronghold so I popped out of stealth. Moving around for awhile made me feel sick, though, because of the change in perspective and movement speed difference, so I had to go back into stealth.

I have a nasty habit of kiting stuff into other stuff and making them fight, even if I'm allied with one side. Then I mop up surviving baddies and loot everything I can. Always lured stuff to Brotherhood of Steel patrols so I could get their power armor. I very much enjoy kiting the respawning Mirelurk Queen to the Brotherhood patrol near Croup Manor, then I'll hide and enjoy the carnage.

I often role-play in my head that my character is a lawful psychopath.

I guess I sometimes save too much, but I'm trying to stop that habit.

Whenever I'm going to get killed, I reload the save and pretend it never happened. That and reloading even if I use 1 round of my 200-round drum magazine.

I reload constantly even when it gets me killed all the time.  I don't learn a lesson from reload mistakes.

Uhuh, so much this.

And the bullets thing.

Me too, inmany RPGs I even save twice on two savefiles or save slots, that's 4 saves at a time.    And many saves before critical decisions, although I almost never go back, unless I really messed everything beyond any chance of fixing it decently, or if a more recent save got corrupted (but the double recent save makes this unlikely).

This too.
In RPGs I like to use powerful spells often, if mana isn't excessively hard to recharge, but in FPS I tend to hoard the most powerful ammos to save them for the hardest fights, and then I use few or none of them even in those occasions, for example the first time I played Quake II, I arrived to the final boss with all the ammos maxed out, then I killed him in a painfully long take cover, peek out and shoot sequence using only the blaster.   

This happened to me not for my fault only, as when I had to upgrade (downgrade?) from Win 2000 to XP as the former's extended support was going to expire, Thief III stopped working, its DRM was constantly damaging XP's optical drives drivers, this prevented Morrowind too from working. I stubbornly tried to make T III work for months, endlessly reinstalling it and the drivers to no avail and I ended up feeling lost in Morrowind. In the end I was able to make Thief III work only getting GOG's DRM-free version, but by then I had already upgraded to Win 7. I was finally able to finish Thief III, enjoying it a lot, although it took steps backwards compared to Thief I and II in many things, but resuming playing Morrowind was painful, a big world with free roaming and so many things left pending, and I haven't managed to finish it yet, anything can distract me from it. Maybe after so much time I fear messing up the main quests (I have the GotYE, with Tribunal and Bloodmoon expansions), as each time I resume playing I just do a lot of sidequests and I don't really proceed in the game.
Although on the portable I hadn't these problems, I stopped playing Planescape: Torment, and each time I try to resume playing it it's hard, I forgot too many things, and this time it's all my fault, as I like that game, but something stopped me anyway.