“Bad or good isn’t the point.” Professor Piper shook her head, and her long, wild hair swayed from side to side. “This is plagiarism.”
“No,” Cath said. “I wrote it myself.”
“You wrote it yourself? You’re the author of Simon Snow and the Mage’s Heir?”
“Of course not.” Why was Professor Piper saying this?
“These characters, this whole world belongs to someone else.”
“But the story is mine.”
“The characters and the world make the story,” the older woman said, like she was pleading with Cath to understand.
“Not necessarily…” Cath could feel how red her face was. Her voice was breaking.
“Yes,” Professor Piper said. “Necessarily. If you’re asked to write something original, you can’t just steal someone else’s story and rearrange the characters.”
“It’s not stealing.”
“What would you call it?”
“Borrowing,” Cath said, hating that she was arguing with Professor Piper, not ever wanting to make Professor Piper’s face look this cold and closed, but not able to stop. “Repurposing. Remixing. Sampling.”
“Stealing.”
“It’s not illegal.” All the arguments came easily to Cath; they were the justification for all fanfiction. “I don’t own the characters, but I’m not trying to sell them, either.”
Professor Piper just kept shaking her head, more disappointed than she’d seemed even a few minutes ago. She ran her hands along her jeans. Her fingers were small , and she was wearing a large, narrow turquoise ring that jutted out over her knuckle. “Whether it’s legal is hardly relevant. I asked you to write an original story, you, and there’s nothing original here.”
Fangirl - Rainbow Rowell

Page 107-108. Yeah, Cath, don't be that douchebag.