I totally forgot.

I actually won a race in Carmageddon. By that I mean I ran all the laps, in correct order, and won the race by taking the checkered flag. One or two of my opponents might have been totaled by other cars but not by me. :P

I figured out how to commit suicide in Karateka.

I also unknowingly committed homicide on Jebediah, launching a rocket without parachutes in Kerbal Space Program.

I found a way to jump outside the barrier in Gothic 1. Too bad there was nothing beside it! :P
I have also entered the closed mine (always in G1) to discover that there is nothing -literally, you keep on walking in a black screen- and I have passed the Orcish palisade in Gothic 2 to find something hilarious. All of them were places not meant to be reached with in-game means, but I did it without cheating nevertheless.

Currently, only this comes to my mind.

In EarthBound for the SNES, I've purchased T-Rex's Bat, Non-Stick Frypan and 3 Coins of Silence as Jeff before leaving Winters.

I do that all the time. :P

In fact, we could start an entire thread on shit like that I've done in Kerbal.

Oh yeah! I should really moonlight as a beta-tester for open-world games. My specialty is terrain-breaking. I've seen inside the wireframes of more mountains than I can count, because I constantly try to see if I can find hidden areas by jumping, etc. My finest moment may have been in Two Worlds II, when I managed to jump into a secret valley. Apparently a failsafe mechanism kicked in, and I ended up at the closest teleport portal...which should have been inaccessible at that point in the game. :)

Current playthrough of Wizardry 8:

I found a good place to rest right before Arnika Road. Just clip through the left edge of the doorway leading out of the monastery, and rest while out of bounds.

Speaking of which, I have experimented with casting Return to Portal while OOB there, and then walking off the area and getting crushed; one time I actually triggered a bug that makes the in-game graphics much whiter than usual until I exited the game completely.

In Daggerfall, I would start fighting the guards with the Mace of Molag Bal, kill enemies to get my strength up, and then get killed because the mace's strength bonus increases the damage enemies do to you.

Also, in Daggerfall, I would buy a ship, go to it, enter the hull, bash the door from the inside, and suddenly have to deal with guards. When attacked, my reputation in the Coast of High Rock region would drop, and choosing to come with the guards would reduce my HP to 1 but would not put me in court, as this region (which contains the explorable part of the world's ocean) does not have any towns, let alone courthouses in them.

Edit: Another one. In Phantasy Star 3, I was able to beat the final boss at a reasonable level without using any TP or consumables.

Teabagging in Halo.

https://www.youtube.com/watch?v=ZYs92_QQoJo

Someone's been playing Stardew Valley, huh? Just out of curiosity, do many members of the GOG staff play it? Just wondering, since the game turned out to be so popular.

Talking about oblivion how about releasing people from my pocket in oblivion:
https://www.youtube.com/watch?v=0dXzePYqeHY
Or the daredevil project v2 for rct3 soaked i made peeps fly from one pool to another.

Taking every object that could be interacted with in Gone Home and placing it in one convenient spot.

At least, that was the initial plan.

Though I wasn't keeping active count, I eventually gave up when I realized that there really is a lot of junk strewn about the house that can be interacted with... way too much of it. My room to drop it all in of choice was right at the start and even though I called it quits, I could easily foresee the entire floor of that area alone being covered in clutter.

And I threw Apple Jacks® at panda bears in washing machines. What has either got to do with video games? ;D

That's pretty funny. A video on the new Carma by GiantBomb did this for first impressions and had the audacity to call the game 'boring'. Well yeah racing in a DEATH racing game is going to be fucking boring, Carmageddon is all about exploration and exploitation, the freedom to pursue whatever you want whenever you want and however you want to do it. Disregard the 'rules' of the competition and just be a destructive cunt. Being boring enough as your dimwitted opponents to go around the predefined circuit and take your measly bonus is your own damn fault.

The original manual for Carmageddon actually says, "You can win this way, but why would you want to!?"