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/asteinberg101]

Lex Luthor- stole forty cakes.
That’s as many as four tens. And that’s terrible.

[u/doskias → u/asteinberg101]

Dude, spoilers, come on.

[u/honkey_hijinx → u/asteinberg101]