One day, just after they had finished their O.W.L. D.A.D.A. exams, Lily went to sit at the edge of the black lake with her friends. After a few minutes, she saw Severus get up from where he was sitting and James and Sirius get up too. James disarmed Severus and called him snivellus, which was a mean nickname he’d made up for him, and then started hexing him. Peter Perigrue and lots of the surrounding people watched excitedly, while Remus Lupin pretended to read his book, but really listened to what was happening. After a particularly mean hex, Lily ran over to where James was hexing Severus and shouted, ‘Leave him alone!’

‘Alright Evans?’ James asked, suddenly very nice.

'Leave him alone,' Lily repeated. She was looking at James with every sign of great dislike. 'What's he done to you?'

'Well,' said James, appearing to deliberate the point, 'it's more the fact that he exists, if you know what I mean ...'

Many of the surrounding students laughed, Sirius and Petigrue included, but Lupin, still apparently intent on his book, didn't, and nor did Lily.

'You think you're funny,' she said coldly. 'But you're just an arrogant, bullying toerag, Potter. Leave him alone.'

'I will if you go out with me, Evans,' said James quickly. 'Go on ... go out with me and I'll never lay a wand on old Snivelly again.'

Behind him, the Impediment Jinx was wearing off. Severus was beginning to inch towards his fallen wand,

'I wouldn't go out with you if it was a choice between you and the giant squid,' said Lily.

'Bad luck, Prongs,' said Sirius briskly, and turned back to Severus. 'OI!'

But too late; Severus had directed his wand straight at James; there was a flash of light and a gash appeared on the side of James's face, spattering his robes with blood. James whirled about: a second flash of light later, Snape was hanging upside-down in the air, his robes falling over his head to reveal skinny, pallid legs and a pair of greying underpants.

Many people in the small crowd cheered; Sirius, James and Petigrue roared with laughter.

Lily, whose furious expression had twitched for an instant as though she was going to smile, said, 'Let him down!'

'Certainly,' said James and he jerked his wand upwards; Snape fell into a crumpled heap on the ground. Disentangling himself from his robes he got quickly to his feet, wand up, but Sirius said, 'Petrificus Totalus!' and Snape keeled over again, rigid as a board.

'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 Severus and muttered the counter-curse.

'There you go,' he said, as Severus struggled to his feet. 'You're lucky Evans was here, Snivellus-- '

'I don't need help from filthy little Mudbloods like her!'

Lily blinked.

'Fine,' she said coolly. 'I won't bother in future. And I'd wash your pants if I were you, Snivellus.'

'Apologise to Evans!' James roared at Severus, his wand pointed threateningly at him.

'I don't want you to make him apologise,' Lily shouted, rounding on James. 'You're as bad as he is.'

'What?' yelped James. 'I'd NEVER call you a--you-know-what!'

'Messing up your hair because you think it looks cool to look like you've just got off your broomstick, showing off with that stupid Snitch, walking down corridors and hexing anyone who annoys you just because you can--I'm surprised your broomstick can get off the ground with that fat head on it. You make me SICK.'

She turned on her heel and hurried away.

'Evans!' James shouted after her. 'Hey, EVANS!'

But she didn't look back.

Severus had called her ‘mudblood,’ a terrible word that some people called muggle borns because they thought that muggle borns were worse than everyone else. Severus hadn’t meant to call her mudblood, he was just angry, but he did call her it and Lily was very upset. That night Severus waited outside of the Gryffindor for Lily. When she finally came out he said, "I'm sorry."

"I'm not interested."

"I'm sorry!"

"Save your breath"

It was nighttime. Lily, who was wearing a dressing gown, stood with her arms folded in front of the portrait of the Fat Lady, at the entrance to Gryffindor Tower.

"I only came out because Mary told me you were threatening to sleep here."

"I was. I would have done. I never meant to call you Mudblood, it just--"

"Slipped out?" There was no pity in Lily's voice. "It's too late. I've made excuses for you for years. None of my friends can understand why I even talk to you. You and your precious little Death Eater friends-- you see, you don't even deny it! You don't even deny that's what you're all aiming to be! You can't wait to join You-Know-Who, can you?"

He opened his mouth, but closed it without speaking.

"I can't pretend anymore. You've chosen your way, I've chosen mine."

"No-- listen, I didn't mean--"

"-- to call me Mudblood? But you call everyone of my birth Mudblood, Severus. Why should I be any different?"

He struggled on the verge of speech, but with a contemptuous look she turned and climbed back through the portrait hole.

From that moment on, Lily and Severus didn’t talk much more and stopped being friends, although Severus still fancied Lily and continued to for the rest of his life.