I played the original Carmageddon (1997) for countless hours and sometimes I chose to win by running over all pedestrians, usually there were at least a few hundreds of them in a single map.

In souls I always kill NPCs for their equipment and typically bring the age of darkness.

I see your Civ nukes and raise by wiping out planetary populations with bio weapons in Master of Orion.

In Sims 2 I had to test what happens when you trap children in fire...

Jurassic Park Operation Genesis. I would purposely release the T-Rex to chase down the tourists and eat them. I thoroughly enjoyed it.

Fallout 1/2 - you get "Childkiller" trait after you start killing children, so, IIRC, your reputation falls drastically, bounty hunters are going after you and most NPCs dislike you (which makes quests and trading harder).

Not many devs have the balls to include that in their games anymore.

OT: wiping out whole planets in Star Trek: Birth of Federation in one of playthroughs (as Cardassian, if my memory serves me), some 20-25 years ago.

All that time the developers spent writing amazing stories and creating incredible cutscenes? Yeah not interested. I skip all cutscenes and dialogue (to a point I couldn’t tell you what most games I play are about) .. there are exceptions with a few games that make me not skip but 95% of the time I skip skip skip. Does that count?

You are a monster, AlliedWithEvil!

NGL that’s a pretty fire gamertag. 

I’ve played TLoU:PT1+2, so whatever the worst thing you can do in those games, that would be my answer. (I avoid any games with such violence nowadays. After TLoU, I had concluded that these games were not for me.)

Kill everyone.