Partly inspired by a story about an add Ravenclaw, and something Wings of Dawn thought of.
"Alright, Ms. Lovegood, you will be writing lines."
"You couldn't be more specific, could you?" Luna said scornfully.
Umbridge smiled sweetly, "Write 'I must not insult the Minister'."
"Too bad it's so easy," Luna muttered with a scowl.
She began to write. Suddenly, a sharp pain caused her to stop.
The words had scratched themselves into the back of her hand.
"Wow, I must admit…that's a very clever form of torture."
"I hope it teaches you not to say such things about Cornelius."
Luna smirked, "Well only a complete moron would not see that every insult about him is true."
"Young lady, I will not stand for this…treason!"
Luna stood up, "The Dark Lord is who you should be following! He would not tolerate the things your precious Minister does, like allowing Mudbloods to learn magic. They are unworthy to even have a wand."
Umbridge paused,"Hmmm…be that as it may…"
"And another thing, why is Dumbledore still in charge?"
Umbridge's eyes widened, and then she smiled evilly, "You brilliant child! Finally someone agrees with…"
"Dolores!" McGonagall, who had just walked in, exclaimed.
"I mean…what are you doing here, Minerva, dear?" Umbridge asked sweetly.
"I'm here to take Luna to the hospital wing. Madam Pomfrey thinks she might have suffered a concussion. It would certainly account for…her unusual behavior, like building a shrine to He Who Must Not Be Named in her room."
Luna cackled madly, "Soon you will see the true power of the dark lord!"
She stood and pulled out her wand, "Stupify!"
The two teachers flew into the walls, and Luna sprinted out of the classroom, leaving the small first year who also had detention that day, to faint in shock.