Educational Decree Number 30: All students must live in the dorms of their birth sex, and use the appropriate facilities for their birth sex.
Most people did not think twice about the new Educational Decree in the Great Hall. It had become customary for students to wake up to a new rule being posted each morning, and most people didn't understand what this decree meant. "Birth sex" was not a term often used in Wizarding Houses, and it wasn't like Hogwarts's sex education course covered it. The only Educational Decrees that caused a stir were the ones that affected Harry Potter and his cohorts, after all, they were the only important people in the school. They were the only people who would grow up to have books written on them.
Nobody cared about the second year Ravenclaw who was currently internally freaking out. No one cared that his entire way of life would be in danger, just because he had it slip that "Actually, Professor, your file is wrong. I'm a boy." Nobody noticed that he wasn't eating breakfast. But, of course, this was normal. Nobody ever noticed him, because his friends were in other houses and he didn't like to create a fuss. He tried to stay incognito, in this new world of magic he had only just become a part of last year, this world he didn't have to live a lie in. And now it was all falling out from under him.
He went to his classes as usual, and though Umbridge seemed exceedingly pleased at his discomfort, he followed her instructions during class like a good student. He figured this would all blow over soon. His friends talked to him in class, and he acted like his heart wasn't beating out of his chest in fear they would figure him out. He was a good liar.
But after dinner he goes to the dorm to find his stuff gone. The other boys are laughing and playing Gobstones. He sighs, and goes where he knows he will be laughed at. He almost wishes he was in Gryffindor, because their dorms had magic staircases that would make it so he wasn't allowed to be forced into this. But he is, and he hates himself for giving up so easily, and he hates himself for being the kind of freak even wizards and witches persecute, and a girl asks him what he's doing there and he stays silent, his stuff already in a corner. Soon he is the talk of the common room. One boy asks if he's a faggot. When he doesn't respond, a girl stage whispers that he must be one of those trannies Umbridge warned her about. Soon people are shouting and he is surrounded and the voices in his head are telling him what made you think being wizard would be any different? everyone hates you, just like they always have, because you're a good for nothing freak who doesn't even have the dignity to just call yourself a lesbian like all the other girls who think they're boys. You're useless and ugly and don't deserve the food you eat, and you're lucky you got this far in life. You're lucky Albus Dumbledore took pity on you, and you have no right to feel like Umbridge is wrong, because she's just trying to make sure you don't contaminate the other children, because for all she knows gender dysphoria might be a goddamn disease. He tries to block that voice out, knowing its his own, but then the reverberating sound of what he was just called runs through his mind, and he is not going to start crying, he isn't.
Soon he finds himself face-to-face with Umbridge, who for some reason was out after lights out, which it already was because he had been wandering the gigantic school for so long. "Out after lights out? Detention!" Umbridge says in the high pitched tone of hers, and he cannot say anything. He hasn't spoken since dinner, and he wonders what detention is like. He tells himself he deserves it. He deserves everything he gets.
The next day is like any other day, only he doesn't eat. He wishes to avoid people, so he goes to the library for every meal and soon find he likes the gnawing feeling of hunger in the pit of his stomach. Besides, the less fat he has, the less that can be wrongly distributed.
Soon it is time for detention. He dreads it, but with an odd curiosity. Umbridge takes him into her office, and tells him he'll be writing lines. He thinks this is a worthless punishment. He'll have to write "I shall not disobey the rules" until it is time to go. He grabs the quill and begins.
It's odd though. His hand stings after he's written, but he likes the feeling. Time passes like it's nothing, and when he has to leave, he takes the quill with him. He stays in the common room, too revved up with the odd sort of energy not eating brings to sleep. He draws on the floor with the quill, enjoying the scars it makes on his body. Enjoying the pain he's giving himself, pain on the outside to match the burning fuel of hatred on his insides.
The next morning Filch has to clean his blood off the common room, and his friends never see him again. There are no more whispers of what might have happened, and Education Decree Number 30 is revoked.