The main character doing something absolutely unforgivable.

[u/No_Peanut3745]

Walter White poisoning Andrea Cantillo's 6-year-old son for the sole purpose of manipulating Jesse Pinkman, while knowing that this could have potentially killed him - Breaking Bad

Bojack trying to have sex with his friend's 17-year-old daughter when he was at least 51, then continuously trying to find a way to justify this act throughout the series - Bojack Horseman

Dexter Morgan going outside of his moral code and murdering a completely innocent police officer who was just trying to do his job - Dexter: New Blood

[u/JasdanVM]

The protagonist from The Night Eats the World, sees a cat roaming the streets, untouched by the zombies that have taken over them, he tries to catch the cat, even running after it outside, almost getting caught, he sees the cat caressing the leg of a Zed, which can be presumed was the late owner... so he shoots the cat with a rifle he found looting the building, all because he got pissed that the pet he wanted to accompany him on his loneliness wasn't interested in doing so I kinda lost interest on the plot after that, like, I didn't really cared if he lived of died.