I was playing Red Faction and I was on one of those parts where you drive around in a truck or Jeep or some similar vehicle. The details are kind of fuzzy (this was quite a while ago), but I remember a lot of ice. I was driving up this curving path with a large drop on the right. Somehow I ended up falling off. I should point out that all I used was quicksave. The button was right there and easy to hit. Better than going into a stupid menu. But anyways, I was about to hit the bottom and, sure I would die, I decided to just go ahead and quickload. Except I hit the wrong button. I pretty much gave up after that.

In WoW I had my assign targets keys bound to f7-f12. One night while tanking I was assigning targets midfight, when my client closed and PC shut down. Instead of logging straight on and explaining what happened I started going through logs, checking temps, trying to work out what caused the shutdown. I figured people would understand a comp issue out of my control, and it's better to get it sorted rather than wait for it to happen again at a crucial moment.

10 minutes later the horrible truth surfaced. I have since deactivated the power key next to f12.

Oh, that's good to hear. I thought I was the only idiot in town.

Rule 1 of RPGs: multiple saves!

I use a rotation of 10.

Stupid mistakes... Well, does this count?

Oh yes. And then, a while into the game, you will start to notice that your backpack is getting incredibly crowded, and that you have to sell some stuff, so you sell these buff points, and just add another few gold coins to your ever growing bag of "never to be used" gold.

Yeah, well, Fallout was actually my first RPG ever. But hey, at least I learned that early.

Who did you piss off in Arulco, man? :D

Playing Skyrim.

Sneaking around with my bow.

See some bandit standing out in the open walking around.

Fire arrow.

Bandit runs closer towards me.

Realises its not a bandit at all

Doing the Rocket Man in the Sky! XD

Oh, it's just 2.13 mod/patch/overhaul/whatever. They really want to kill you there. First time you liberate Drassen the queen sends special forces to pacify it.

Yes, three games made me do that: Gothic I, Fallout and Fallout II.
Fallout because of The Glow.
Fallout 2 and Gothic I because of corrupted save games.
Recently had to stop a playthrough of Arcanum as well because of a corrupted save game :(
Even having multiples did not help to salvage it.

e: I typically use a rotation of 3 and also make a separate slot every milestone or so.

Actually one of my iron rules in RPGS with loot drops is NEVER. PURCHASE. ANYTHING. I don't care how much gold there's in my pouch. I'm not giving those greedy merchant a single coin unless I have to.

Another consequence of my repeated mistake is related to this. I always want to get the best deal I can so I end up wasting skill points or experience on bartering skills. It's so stupid but I do it every time.

Heh, I have a juicy one but it is not in-game thing. Long time ago I bought Burnout Paradise on Steam. I played it only little and forgot about it. Few months ago I decided to finally play it but you have to login (to Paradise City servers) when starting the game and when I logged in, it told me my product key is already used, to contact EA support and shutted itself down. I guess it was related to migrating account to Origin or something similar. I tried to contact support. I described my problem and asked them what am I supposed to do. Some Indian person replied to me with some generic mail asking for my Origin order details. I again explained him my problem and said him I have no order details from Origin. He replied with almost exactly the same mail, asking me for my order details. I ignored him and uninstalled the game. This week I stumbled upon another version of Burnout and as I wanted to play it and as I already bought it before I downloaded it. I installed it and it turned out is is czech version and, in my opinion, bad czech version. So I installed the game on Steam again and I tried to copy language folders into the czech version but it didn't work. By then I was ready to commit some acts of violence but instead I booted up the Steam version again just to try it. I started to insert login details again but I wanted to change something in them so I pressed Backspace only to discover it allows me to bypass all that login crap and I can play the game just fine. So I went through all that hassle and it took me several months only to find all I I had to do was press Backspace. :-p

Also I am guilty of almost all things you mentioned here recently. I tend to hoard money, I tend to hoard potions or special ammo (fire arrows and stuff), I try not to buy things from vendors, I often don't use best weapons in FPSs to save ammo for difficult fights

Had a somewhat similar problem.... After a really tough mission in WC (that I'd played 8-9 times and FINALLY won), I forgot to request permission to land . . . . ran head long into the Tiger's Claw . . . . and boom....