It's clear why everyone hates Cersei Lannister: it's her resting bitch face. Ok, so more diplomatically, her father wasn't particularly nice to her, marrying her off to a boorish man she had no interest in, who routinely cheated on her, but it's no excuse for that expression. Her affair with her own brother is, of course, creepy, and she loses additional points for raising the demonic Joffrey. She mothered and manipulated him into the monster he became, and while she clearly loved him, that makes things even worse. Quite how she raised Tommen is a mystery. Her constant sense of injustice is a major source of irritation, as she encounters problems of her own doing, then complains about them and schemes until somebody loses their head. Her sickly smile after the death of Prince Oberyn has only added to the resentment fans have for her, while her endless torment of Tyrion is particularly poisonous. It looks like she'll be running into difficulty now the Lannister position in the kingdom is less secure though. Fingers crossed anyway.
