Remembered a couple more, which are kind of related.

Bioshock - killing or saving the Little Sisters. There was no way in any shape or form I could bring myself to kill the girls. Not even once as let's just see thing. I did watch a video on YT and it made me feel sick.

Likewise, the Fallout 3 DLC The Pitt storyline requires you to decide the fate of a group of people and it hinged on the life of a baby. There was no choice involved for me. I would sacrifice adults to save a child. There may be arguments against my view but there was no way I could raise my hand against a baby.

Killing children is a NOPE for me. Won't do it, can't do it.

Yeah, I didn't know that in the first session of the first game and nobody knew this game back then who could have warned me. I learned it the hard way. :D

I installed a mod that unadvertisingly modified cliff racers in Morrowind with ranged combat abilities. Early on, they were instant death machines, shooting out multiple affects at once. It took me a very long time to track down the mod. At first I tried to just avoid them and they became the most dreadful and annoying creatures. I finally found the mod and it was a massive new land and quest mod... but was totally worth disabling to get the cliff racers back to normal.

Second runner up is almost all bosses in computer games. The need to make each battle more difficult than the last has yielded some pretty ridiculous scenarios. This implied mechanic takes most decent games and tarnishes their fun with an exercise in extreme frustration at the very end. I always hold up the Thief series as the way to do a boss battle. They didn't change the gameplay expectations at the very end. The game kept its identity even in the "boss" battles.

Does it count if I just don't want to do it? The pressure plate maze in Penumbra, I just got too frustrated.

Why the fuck would anybody do that!? "Oh I've got an idea, let's change around the most annoying creatures in videogame history so they're not only annoying but also deadly!"

Maybe I should desinstall the mod that replaces their screams with justin bieber songs.

http://www.youtube.com/watch?v=S4rXsrZRchQ

Skyward Sword: Having completed three dungeons, it is now your task to prove your worth of the Mcguffin with this totally bull test that should just be skipped since we need you to save Hyrule.

It doesn't help that I was already displeased with the game up to that point and was having issue with the desert of the damned, having ignored the nag of a robot they gave you, nor did it help that I had read Hyrule Historia and felt there were several design choices they could have made better while openly showing you better designs they didn't choose, and the whole timeline unification was rather a slap in the face, but just finding myself in yet another stealth section in a game that wasn't built around stealth broke the metaphorical camel.

Tears of Light in Twilight Princess? No problem, they've actually been separated from the entity that needs them to restore the land. Triforce Shards in Wind Waker? Don't see why anyone complains about that so often. Actively withholding items the hero needs to save the world and being unable to recognize him yet having designed him yourselves? I quit the game, so unless that was explained, I dearly hope the Goddesses were plastered and simply lost their sketchbook, and not a metaphor for how distant Nintendo is with their public. :B

Stealth in non-stealth games tends to be a bit of a stopping point for me in general. At the very least, let me knock the guards out, don't just throw me out!

I'm stuck in Terranigma for such a reason. (It doesn't help that the guards seem to turn randomly, rather than following any pattern.)

I completely forgot about that until you mentioned it. I remember getting to that part. I can't remember what I chose, but it stressed me out. Now that I think about it, I think I stopped playing the game after I finished that DLC.

As for my own moments... The sewers in Amnesia. I have gotten through it both times I've played the game, but I always have to take a break (at least a day long) after the sewers because I end up with a headache. It's horrible.

Dark Souls' Blighttown the first time I played it. I struggled through the game up until that point, but I had so screwed myself over in leveling up that I just couldn't go any further. I gave up and started the game over some months later. I still had a hard time, but I made it through okay. The Four Kings almost made me give up again, but I stuck with it.

Dragons in Dragon Age Origins. I'm thankful the only dragon you are required to fight is the end boss, because the two dragons (the only ones I know of, anyway) that you can fight earlier are ridiculous. I tried both, and neither turned out well. To be honest, the difficulty in that game is all over the place throughout, but those two fights are especially bad.

I'm sure there are some other things I'm forgetting, but those are the ones that stuck out.

Ravenholm. Took me a few days to beat it, where I only went a few hundred feet then took a break from the game. :P

Blitzball in Final Fantasy X. Nope. Just big NOPE. I tried to like it, but I wasn't able to.

Heh, I actually managed to lose on the very first turn of a Fall From Heaven game. Created my capital, had my warrior explore an adjacent ruin, which spawned an enemy directly on my undefended capital. I couldn't have lost faster if I tried.

Hearing this.

Though Audio Atrocities explains it much better than I could:

«Exhibit A: “You can't run away.”
We may not be able to, but this falsetto transsexual delivery certainly makes the urge to run strong.»

-- Shining Force III, Sega Saturn

Those skeletal, undead swordsmen in Thief Gold really creeped me out. They were very quick and had that disturbing laugh, and it felt like I couldn't escape them once they spotted me. When they did spot me, I'd hurry to re-load an earlier save because I just found them too disturbing. I found that game more unnerving than System Shock 2.