Question: Why did Lily never accept Snape's apology for calling her a mudblood? He never meant it as it was said in the heat of the moment.
Answer: Remember how enraged Ron got when someone called Hermione that? I get the impression 'mudblood' is the wizarding equivalent of the N word, and there are just some things you can't take back.
This is a good answer. It also should be noted Snape was already on thin ice with Lily as he was into dark arts, showed signs of intent to become a death eater, not to mention according to Lily he had been calling others of her birth the same name. This was the straw that broke the camel's back for her.
Answer: Rather than "heat of the moment", it was more like "the straw that broke the camel's back." Snape was friends with other pure-blood supremacists, who would later become Death Eaters. They bullied Muggle-borns. In the book, she asks him: "But you call everyone of my birth 'Mudblood', Severus. Why should I be any different?" Essentially, Snape had chosen his supremacist friends over her. He refused to stop joining in their behavior.
Answer: I think it was Hermione who said "it's the worst thing you can say. It means dirty blood" Lily is deeply hurt by Snape saying it. It's similar to a modern day argument. Some things just can't be taken aback.
Ssiscool ★
Good answer. Would add that Lily's hurt and disgust also stemmed from Snape calling her that after she had befriended and defended him against cruel students, including James Potter and Sirius Black. Snape turning on her that way and his increasing dark beliefs were too much for Lily.
raywest ★