I Civ 3, every time I played without failing I would nuke Birmingham and only Birmingham continually, because I had a teacher by that name and he was an idiot.

Postal 2, no further explanation needed for that.
Actually, you really cannot not do anything sick in that game. Everything is based around that..
Using cats as ammo for the shotgun, and urinating on people after setting them on fire, and in the end decapitating their head from their body with a shovel, is without a doubt the most disturbing thing I've done in a videogame.
(Postal 3 looks like utter crap by the way.)

When I played The Sims, the first version, I used to torture the whole family by placing loudspeakers next to every bed, playing music 24/7, and blocking the toilets once in a while.
I also trapped one in a room, speeding forward time until he/she died, then did the same with the rest until everyone was gone.
Kind of sick when I think about it. o.O

You could be really cruel in Black and White also.
Not only could you slap the poo out of your creature for nothing, but you could also kill villagers by picking them up and hurling them into mountains and stuff.
Even children, if I remember correctly.

But I always felt like crap when I slapped my monkey creature in B&W. I love animals and their expressions of sadness made me feel terrible. :(
Kind of hard not to do it though when you have the option. >_>

Personally I've never liked Postal 2. I just didn't find it to be any fun. But it certainly has enough sick stuff to do.

Sick acts?

I've killed people.

I've a really hard time doing mean things in video games. I get too immersed when I play and being evil feels incredibly uncomfortable.

Even in Overlord I was pretty consistently good.

This made me laugh, I especially like the fact you did it to your girlfriend. Nothing like computer games for removing the trust.

Now I kinda want to blag my way onto the GOG terraria server, brick up the mineshaft, then fill it with lava. Stand outside the bottom of it and watch people desparately trying to dig themselves out of it before they die. I'm not in any way evil.

She's rather used to me doing stuff like this. The problem is she doesn't quite know what to expect, hehe.

Trolling the GoG terraria server would be fun, as long as it wasn't destroying anyone's hard work and merely something amusing. I trolled a minecraft server that had this giant computer system installed, once. I rerouted a single pipeline in the middle of it, so that anything it would calculate would either break the thing or give a wrong result. It was something they got from a savegame anyway, so I didn't really destroy anyone's hard work, but they had no idea why their cool thing wasn't working properly and none of them had the expertise to fix it, so it just stayed there, bricked. The fix was only as complicated as removing a single block.

letting meryl die so that i can get the stealth cameo :D

I flipped off a box of kittens once so Morrigan would like me.

In my defense, she's voiced by Claudia Black. I would eat that box of kittens live to have Claudia Black look at me.

I love doing pranks, as long as they are just amusing and don't actually hurt anyone/destroy someone's hard work. I have a real distain for Minecraft griefers, unless they do something that's truely clever (like what you described) and isn't going to actually effect the world (like if they have saved games, etc).

oh.

i once as a medic in TF2 didn't heal my comrade who was in flames.

it was funny as he spammed the medic button and was waiting for me to use it and he knew i wasn't a spy.

I played TF2 on server where there was custom things that were said each time some made awesome thing...I once had 13 kill streak with pyro and the server told me : Detlik is Sick Freak, someone get a ban stick.

When you're good, you're good.

When you're being accused of cheating, you know you're GOOD.

I thought of another one, the first child you see in Deus Ex, I drown him every time after I give him a chocolate bar.