Do you have any quirks related to gaming?

no, nothing.. quite boring, as I am as a person probably

If I find a bug in any game, I tend to try and push to replicate or worsen it

Methodically exploring levels. Became obivious whilst playing Colonial Marines Co-op, i´m still going around to see every corner - BOOM - someone else triggers a savepoint/cutscene, again :E

I do the same :D

I don't play racing games very often, but my husband is into them. So whenever we play and I'm driving around a curve I lean to the left or right as if I were in a real car :p

I sit sideways on my chair when the game's difficulty isn't hard and sit properly when things go serious.

I lean forward as the difficulty increases.

I click on the game I want to play in my Steam library, but will use the game's desktop shortcut.

Oh boy! Let's see...

I lean when doing tight turns in racing games.
I completely fill in all maps even if it means dragging my face against the walls and walking through lava for no reward.
I talk at games with silent protagonists.
I stick my tongue out when in need on intense concentration.
I collect everything and anything. I will go back to town to store/sell off excess items and then go back to keep grabbing everything. On the flip side of that, I don't use items unless it is the only way to progress.

There's probably more but I can't think of them right now.

I generally save before each major decision and check each option, then make another save for each one before picking the one I liked best.

i spoiler every person i know the ending... :3

the only thing "I" realize doing is watching the whole credits as a sign of respect for the makers... if i hate a game i dont do it.. >:P

I'm a "save" maniac.
In some games I save after taking a few steps. I even save after staying idle for a little bit.
In open world games with collectibles/upgrades, I like to get all of those before proceeding with the main story.

I love to jump everywhere to go off-limits. Not always a bright idea as it can bug the missions or even the game. Sometimes you just end stuck into a rock 30mins after the last save.

Like others have said before me...complete all available quests I can find, take all the loot possible and finally save wherever possible. Have never installed one of my steam games intending to just idle it for cards. I genuinely try to play the game as best I can (but my best is below par so some end up idling for that last card drop :)
And I draw maps with paper and pen when I deem the in-game map is insufficient. Love the games where the map fills in as you explore...hate it when there are no maps at all)
Edit: Forgot about the finish. Once done I categorise the game and uninstall. All my games are in the default "My Games" section until I have finished with them, then they get sorted.
(Re-reading this I sound a little anal...I am not, I swear).

I will do a mass-murderer playthrough in any game that allows them (so, most western-RPGs or games that draw a lot of elements from those), just to see how the game responds. In older games, things get outright surreal with people not noticing you just shot everyone around them in the face and such. Newer games tend to call you out on this more but it's still weird how often actions don't have lasting consequences.

Whenever I finish a game, I smoke a cigarette and read all of the credits, because I feel the people who made the game deserve that. If that counts. Not that much of a quirk, I guess. ^^

I suffer from OCRD, Obsessive Compulsive Reloading Disorder, I am compelled to reload my gun after almost every shootout even if I still have (sometimes much) more than half a magazine/clip or whatever, usually resulting in my death when another enemy shows up and catches me with my pants down.

I think I have no habit that's very characteristic of me. I love searching/looking for secrets or loot, I'm impulsive in a way that I want to go to X place, I try to climb to somewhere, die to see if the barrel explodes, etc. But this is just common curiousity I think :)

After reading other people's comments and thinking about it thoroughly, I can safely say I'm an achievement whore, I like getting all the achievements that I can in the game, and if I miss some of them I do another playthrough a few days later; I like the challenge of getting them and also achieving 100% in the game. I also like to explore and find out every single thing I can in each level/map.

I save (hoard) valuable consumables for later...and never end up using them.
Speaking of saving, I tend to save my games a lot, ending up perhaps spending as much time saving as playing and with tons of save files I'll never load again.

I always feel like a game might have secrets and that I need to check every corner of a level before I continue... even if I'm being timed or have low health or whatever.

In single player, I almost always hoard ammo, even when I could really use it. If I have a melee option or some alternate way to take down a hostile, I will typically go through extra pain to use it. Only when I'm nearly at max ammo for something will I start using it (and will tend to force myself to use weapons I have max ammo, when there is an ammo pickup for it nearby). I'll preserve perishable smartbombs and special weapons for as long as possible. Can't even remember where I picked up the habit, but it certainly came in handy when I got around to playing Vanquish where you can upgrade weapons by picking up the same weapon more than once, providing the first instance in your inventory is at full ammo (but you need to do this several times to upgrade to the next performance boost).

In every single game where there's a toilet, I always try to interact with it to see if I can flush it (and end up disappointed if I can't) :D