In Civilization I used the world editor feature to create an army of tanks and just invaded everything and I completely slaughtered villages.

I'm generally a nice person.

In Ultima Online, I turned 10,000 gold into 7,000,000 in a few weeks with a duping bug, thereby contributing to the insane inflation that happened in that game when I pumped the duped money back into the economy. As a side note for those who've never played ultima online: It took a long time to get one million gold legitimately let alone 7 million.

I would also kill miners' pack animals in town and steal their ignots when they tried to carry it themselves.

Amn-wide massacres in Baldur's Gate.

In Fallout 2 I tried poisoning Vault City's mayor, then I had to exterminate the whole town. In the same game in New Reno I was caught after banging Bishop's wife and daughter and had to kill almost all the "family". I didn't really repent, the first were a bunch of hypocrites, the second gangsters, but I had to reload and undo the first thing to avoid breaking some quests, while I reloaded in New Reno, but just to try again to bang Bishop women until I managed to avoid being caught. Bishop's daughter called my bluff anyway and bore a grudge against me for the rest of the game. Besides getting pregnant.
In Thief III I stole also the money left from the Abysmal Gale's captain to his widow to reach 100% loot.
In Gothic I unnecessarily killed some human foes after defeating them, to collect more XP.
In Planescape I revealed Silent King's secret to Acaste, triggering a bloody ghoul riot, but after enjoying the massacre, I reloaded to undo it, to avoid having skeletons and zombies hostile.
Normally, anyway, in RPG's I try to keep a good alignment, although I choose or reach (if dynamic like in Planescape: Torment) lawful too only if the best weapon I like in the game requires it, otherwise I prefer neutral or chaotic good.
But in Quake II I found very sick that some space marines asked to be killed after being freed and having to actually kill one to reach a secret area he was obstructing.

Edit: Ah, I also tried "Vas Kal Corp" in Ultima Underworld - The Stygian Abyss, but it destroyed everyone and everything but me, but including every item and the links between levels, so it was totally unsatisfying...

Taking a screenshot of Peach's undies in Super Smash Bros. Brawl.

CGI-Quality said: Beat an old lady to death in Saints Row 2 I'm serious, I felt like crap afterwards............

Lol! I was just trying to think of any nasty stuff I have done and you reminded me of one.

In Saint's Row 1, there was a granny limping down the street using a zimmer frame. I approached her and randomly hit her with a baseball bat and she fell to the ground. She then stood up and preceeded to sprint down the road like a Jamaican Athlete dodging all of the oncoming traffic.

I gave chase for a short while untill she ran straight towards a very tall wall (atleast 10ft). She gave a mighty leap and grabbed the ledge and hoisted herself up. While this was happening, me about 20 meters away laughing pulled out a grenade and through it towards her direction.

Just as she pulled herself up and was standing on top of the wall my grenade clonked her right in the back of her head, causing her to front flip straight of the wall onto the otherside out of my view.

I was to busy pissing myself with laughter after this, she provided me to much entertainment so she deserved to live... Untill I realised my grenade bounced over the wall with her. A few seconds later I heard a explosion followed by a loud scream followed by granny cartwheeling through the air.

The only others I can remember are not so funny. Shooting Rachel and Sonia between the eyes with a Arrow in Ninja Gaiden and Ninja Gaiden II.

GAME OVER.

well as long as it wasn't a coochi poochie puppy thats not too bad!

Off the top of my head, I shot the dead baby in Max Payne. Aside form that, A TON of stuff in morality games like Fable and KOTOR 1&2.

Man you guys are evil, I don't know what the worst thing I have done, nothing really pops up.

I played LAIR.