1. Myron - Fallout 2
As we've already established, while it's not surprising that games set in a world wherein merely surviving into adulthood was something of an accomplishment that human ethics aren't at their most virtuous, Fallout 2 takes the shamelessness of humanity to a whole other level.
This is possibly best personified in Myron, a teenage that the player encounters in Reno city. Myron is allegedly behind the invention of the drug Jet for the Mordino crime family, resulting in a huge number of the surrounding residents to become addicted.
However, while Myron's lack of remorse over his creation of a drug that has left countless people hopelessly dependent is disgusting, the teenager commits an even more sickening crime in-game.
If the player character is a female with low intelligence, Myron will knock the player out with a spiked drink when they first meet him... and then proceed to rape them.
Yup, the game really went that dark.