"LEAVE HIM ALONE!" Lily shouted. She had her own wand out now. James and Sirius eyed it warily.
"Ah, Evans, don't make me hex you." said James earnestly.
"Take the curse off him, then!"
James sighed deeply, then turned to Snape and muttered the countercurse.
"There you go," he said, as Snape struggled to his feet again, "you're lucky Evans was here, Snivellus-"
"I don't need help from filthy little Mudbloods like her!"
Lily blinked. "Fine," she said cooly. "I won't bother in the future. And I'd wash your pants if I were you, Snivellus."
This is from the Snape's Worst Memory chapter in Order of the Phoenix. I cry so hard everytime I read that scene, especially at this part. My keyboard is wet with my tears as I type this. No joke.
It makes me cry that Lily cared about him so much before, and because she never forgave him even though I bet she still cared about him. And it makes me cry that Snape said that only out of anger and humiliation. And it makes me cry that Lily ended up with the man that ended her and Severus's relationship.
I bet Lily was the kind of girl that was really smart, and also really stubborn. She relied on logic and solved everything, but no matter how much her brain was telling her that Snape was a bad person to be around, they had been best friends forever and her heart refused to give up on him. Hearing him call her a Mudblood was like hearing him say 'I hate you.' And that must have made her so sad, but she didn't want to cry in public. So, the only way to keep from crying was to be angry, which she was. She wanted Severus to feel as bad as he made her feel. At least, that's my theory.
I must go now, because I'm crying too hard.