Most cartoonishly evil choices in games?

[DiceByte]

The fact that in the Doom add-on “Rekkr” or something like that you can kill the innocent rabbits running around

 

[OliveTree]

its already been mentioned but harvesting the little sisters in bioshock really does have to take the cake, i feel like

[DogsRNice]

Here's one that's kinda out there and evil if you consider deliberate inaction to be evil.

 

At the very beginning of super paper Mario after you get told the entirety of existence is threatened and only you can stop it there's a dialogue choice to continue or not. If you repeatedly say no then you get an instant game over, which implies Mario really did do absolutely nothing and everything ended. Just to make that worse, later in the game you go to the dimension that houses heaven and hell and find that it's also doomed to be erased so even people in the afterlife won't survive... 

 

Rated E for everyone 

[The BMFG]

in my fallout new vegas playthrough i killed almost every single npc i ran across and by the end nearly every faction hated my guts 

[Lucius Wooding]

I'll just say that good old tabletop RPGs are way more interesting and allow more creativity than any video game when it comes to being an asshole. Because although Bioware may have talented writers with good ideas, the real expert on dice fueled dickery is me.

 

I rarely play completely evil characters but sometimes you can really tee off on the morality scale and make renegade Shepard look like an absolute choir boy (or girl). Or you can just create a magnum opus of mischief for the lols. I've been playing good and bad characters for 20 years and DMing and being able to come up with your own blue dialogue options completely torpedoes anything scripted. There's nothing better than making the DM go "OK roll your persuasion check... Actually better make it intimidate", or making the whole table laugh at how over the top your actions are.

 

Spoiler

-In a homebrew pokemon campaign, I came across a wild pidgey while fishing that hopped up to me curiously. It smelled french fries on me since I was too cheap to buy actual oil to fix my reel, I had snagged some used cooking oil from a restaurant instead. I had no intention of catching such a common pokemon, and nothing to give it, yet I saw an opportunity to be an absolute dick for no reason. Pretending to get food from my pack, I then sprayed it in the face with water from a bottle and laughed at it in triumph. This backfired due to me having a totally untrained party at that point, as it rose up in wrath against me and attacked for some reason. I had to run for my life and waste a pokeball just to buy time to make some distance. It was actually the second or third closest call I had in a long campaign, and that character held a stern grudge against pidgeykind from that day forward.

 

-In the same campaign, I had been attacked on two occasions by a wild golduck with a cadre of psyduck near my fishing grounds, and lacked a good counter to them so the fights went somewhat badly for me. I later discovered they used a nearby sea cave as their lair and swore revenge. Along with a sadistic female psychic who specialized in turning other beings into puppets, we ambushed them at night and she forced them to infight. By this time we both had strong pokemon and had the upper hand, knocking out and capturing most of them and enjoying every moment of it. We then sold the unwanted psyduck on the black market and used their cave as a base of operations for some time. 

 

-Later still, I was fighting someone on a boat at sea who I really didn't like, my main nemesis in the campaign. I was a psychic teenager and he was an adult mercenary who carried a gun as well as other weapons, having shot, killed, and kidnapped other psychics before. So he was scary, but I'd killed and wounded some of his men before and this time I had him at a big disadvantage since I had him ambushed and outnumbered, as well as showing up riding on the back of a very pissed off Lugia. I came up with a solid pre-ass kicking one liner before sinking his boat: "I'm sorry we couldn't be friends, but at least I'll get to turn you into chum." 

 

-In a fey-themed carnival in a D&D campaign, I caught a flower from a performer. I found a small child and I traded it to them in exchange for currency, tricking them into thinking it could grant a wish when it was completely ordinary. Note that this provided almost no value for doing so except to be a dick.

 

-In the same carnival, I talked a pixie who worked there into letting me shoot her from my bow because it'd be a cool stunt. She got hurt after landing halfway across the carnival. I then tracked her down and apologized, and we worked together to pretend it was actually fun and manipulated a different pixie (with a stuck up attitude) into performing the same stunt. 

 

-I was playing a pacifist noncombatant npc for a short time and used my most powerful spell on an ordinary bee that stung me. It didn't directly harm the target, but caused it to be overcome by nightmarish visions that drove it mad and caused it to die from terror and guilt. I was the only one with Speak With Animals active so nobody else noticed it, and I got to hear its final desperate words. 

 

-In a one off session where I was completely evil, I started a tavern fight for no particular reason so I could kill the whole town. I had a small acidic ooze as a familiar, not big enough to do much fighting. But when the bartender got knocked down, I dropped it onto his face where it dissolved and digested his face before he died painfully.

 

-In a Star Wars campaign I impersonated a well known bounty hunter on multiple occasions, trying to bluff my way through situations as well as deflecting all the heat onto him even though we didn't know each other. I was a low level peon doing it for my own amusement more than anything. Eventually I befriended a hutt crime lord because he liked my sense of humor and unpredictable nature, as well as the sheer balls I had causing trouble against those bigger than me. The bounty hunter later confronted me in the hutt's palace over all the misdeeds I committed in his name and was about to kill me, but I managed to drop him into a rancor pit mid monologue (as one does, all hutts have one) where he was quickly devoured. The hutt was so amused he wrapped a box of thermal detonators for me as a present.