Many years ago I made a bet with my friends: I was supposed to finish Another World without dying. After some training I won the bet :D

Hmm... Well, I did spend a day in Witcher 3 running around Novigrad in my underwear and a King Radovid mask.

-Accidentally changed my character's sex within the game in Dark Souls 2 and changed it back
-Called in an airstrike and ran into it (in Dirty Bomb)
-Got stuck with a sticky-bomb to the face and ran towards the medic to revive me after my death and killed the medic along with myself when the enemy detonated it(, also in Dirty Bomb)
-Got S Rank, the Foxhound Badge, bonus for No Reflex, bonus for No Kills, bonus for Perfect Stealth, No Kills and bonus for 100% accuracy because I didn't fire any shot in the last mission of Part One of MGS5: TPP
-Went through the entirety of Splinter Cell Blacklist and Chaos Theory without alerting anyone
-Watch too many times my teammates running into the room I just threw a nade into without it exploding in Insurgency
-Trying (because I still do this sometimes) to pick up thrown live grenades thinking they're pinned grenades that fell off dead players (in Insurgency)
-Doing the same with C4 packets and IEDs (in Insurgency)
-Sneaking up on and killing with Phantom and his katana the snipers that wronged me even though I die to their team mates a few seconds later(in Dirty Bomb)

 ▪  <span class="bold">Sims 3 - Who Drowns First?</span>    :-)

I thought of another one:

In Baldur's Gate 2, with a bit of cheating I managed to kill the guy in the tutorial. I did, however, need to use the HLA "Greater Deathblow" to accomplish this, which means the Throne of Bhaal expansion is needed. (Cheating is actually not necessary; just raise a fighter-type main character to a high level, learn Greater Deathblow, export that character, then import the character to the tutorial.)

Of note, this particular character is, I believe, immune to all weapons regardless of enchantment, so using Shapechange to change into a mind flayer won't work here.

Spent whole day in GTA San Andreas, running around the lighthouse and punching people to death to collect their money, so I could buy an apartment/house on the very same beach. Did so because police wouldn't start chasing near the lighthouse, unless some big weapons were used or explosions and mass killing.

Eventually, I got enough money, bought the house, went inside, thought "Uuuh, nice floors! So shiny!" and went to sleep.



Now that I think of it... I better would have just cheated...

Arx Fatalis. I was disgusted with the world itself, the npc personalities, the hypocrisy, all the dirty little secrets and since i had the power and the game didn't punish me, just before beating the final boss, i went through each and every level, killing, burning and exploding EVERYTHING that lived. Down to the very last mice that cannot do battle with you (but can be cast incinerate on)! I even killed Alia and the King, the snake women, anything being alive, no exception. And then using the Douse spell, i even put off the lights from everywhere, for good.

After beating the evil god though, that fat divine bastard still congratulated me for saving the world. Even though i made it go extinct...

I don't know if it's absurd or weird but I often stop and look at ceilings, check if they have windows or paintings. I've always interested in interior and exterior level design in games, in some cases more than the actual gameplay. Good example was Unreal, I didn't like the combat for the most part but everything else was well worth it.

After my first playthrough of Deus Ex: Human Revolution, I started over on the highest difficulty, and I have not killed or alerted anyone the whole game. Weird as it may sound, this way the game was a lot easier to beat. The same thing happened with Batman: Arkham Asylum, after betting the game once, I started again on hard, and I did most of the riddles as soon as I encountered them, this way I had access to most of the upgrades pretty fast and the game was a lot easier to beat.
I heard a monster coming in Amnesia: The Dark Descent so I blocked the entrance with every object I could find in the room. And then, the monster broke the door, but he couldn't get inside, so I stared at it, since usually I don't have time to look back while I'm running away.
I went a little overboard in METAL GEAR RISING: REVENGEANCE when it came to cut my enemies, I cut them up in so many pieces that my CPU couldn't handle it after 600 pieces.
I farted on most of the characters from Fable - The Lost Chapters, I still have no idea why.

Washing the dishes (The Sims 2).

Why? Because, in my oppinion at least, leftovers (crumbs, sauce etc. ) are the most disgusting thing on the planet

Fill a church with cheese in oblivion...shift thingy...kinda poopz, that's all i've got...meh.

Finished the human and orc campaign in the first Warcraft without any knowledge of the game's drag-select.

XD
Along those lines... Played 10 chapters (out of 15) in NOLF2 before realizing that I could spend skill points :-| ... It was a totally unfamiliar concept to me. I had never played a game with skill points before that.
Same game - I liked to break all of the toilets in guards' patrol areas, so they would panic and run outside to pee :-)

I threw washing machines at panda bears in Apple Jack.

Ah this is killing me1 I'm pretty sure I did that too in some game with skill points, but I just can't remember what game it was :P