Worst things you saw happen to you in a game.

Getting processed into a Strogg in Quake 4's single-player campaign.

More interactive: My first encounter with Mutons in XCom Enemy Unknown. And finding out that they carry grenades, which means that from that point on it's a really bad idea to keep your squad bunched together.

the eye scene in dead space 2.
i hate it. the sole reason i don't want to play it again.

Getting beheaded in Skyrim Special Edition(unmodded) ... way to trigger the execute animation while I was at half of my hp...

I will not spoil it, but the ending for Braid.

The ending was both the worst thing to happen to your character and the best thing to happen from a story perspective. I sat silently in awe for I don't know how many minutes after that.

This.

It was a glitch, not supposed to happen normally as this kind of zombie type isn't supposed to be able to reach the roof anyway.

Luckily we still managed to win the game.

I was in a 3v3 tournament with 2 of my friends in Bloodline Champions. We breezed in to the finals and then one of my friends got drunk with power and used both of his escape/mobility cooldowns to instantly get right in to the middle of the map the second the round started, leaving us way back out of reach. Enemy team saw that he'd put himself out of position and just zerged him, throwing us the round and tilting us in to losing the series. This was some 5 years ago and it still gets brought up every couple of months.

Sweet classic Naxxramas days in vanilla World of Warcraft: Noth the Plaguebringer boss encounter. Taunt had a chance to miss back then and my stupid taunts kept missing so summoned skeletons went on to kill healers. Therefore causing the death of the entire raid because my taunt missed. Fortunately I am not the only poor tank this happened to :P I'm glad taunts don't miss anymore :D

This wasn't something that happened in a game, but something that happened to my savegame.

A loooooong time ago, I played Ultima IV on my Commodore 64. I was at the entrance to the Abyss, and just needed to figure out what the final word was that I needed to type in that would complete the game. Since save games were limited back then, I could not save at the bottom of the Abyss, as you could only save "outside". I lent my discs to a friend and said to NOT start a new game as it would write over MY savegame. I get the game back, and what do I see? A new character at the start of the game. I really wanted to punch him after that!

As for in-game things? The ending to Over The Hills And Far Away hit me like a ton of bricks.

Getting smooshed into jelly by a Supermutant Behemoth in Fallout 3 was one of the bloodiest ways I've died as well.

any scene when you fail QTE in rebooted Tomb Raider - it's like torture/gore-fest ;p

Mass Effect 3 ending. I spent a whole evening thinking about what I should do. I'm still mad about it even though I am sure I made the right choice.

A certain, fully first-person unpleasant experience for the player character near the end of Bioshock Infinite Burial At Sea part 2. Won't mention it because spoilers, those who have played it will probably know what I'm talking about.

I should probably also mention that I'm a synesthete for pain. As in, when you see someone (yes, even in movies or videogames sometimes) get injured or listen to them describing the event, you feel pain as well. With the awesome difference that their bodies will react to the (real) injury by releasing natural painkillers as it should, while your brain deep down knows you are not really in danger, so it makes you feel pain but it doesn't release anything to soothe it. Because screw you, that's why.