Author's Note: This is a copy-paste of a story written by an Anonymous user on 4chan (written on 03/15/17, on a Gravity Falls thread). I have permission to post this from the Anon himself, for the sake of posterity.

As far as anyone is concerned, Dipper and Mabel are of legal age in this fic.

UPDATE [01/10/2017]: Changed the paragraph structure a bit, made small corrections, and added a few words. Nothing special. Also, to the Guest reviewer: Yes, I agree, I also see it in Mabel's character to egg Dipper to do stupid and retarded shit; DP's short-haired Mabel also makes me hard as a rock, most of DP's work does that, to be quite honest, she's what got me into Pinecest (even though I used to hate it with a passion).

'FREAK'

Dipper stared intimately at the word, sprawled across his locker with some kind of foul red paint. His fingernails explored the few strands of hair that had sprouted from his chin as he wondered whether he should bother getting a teacher to clean it up this time. If he kept it up there wouldn't be room for his classmates other favorites like "Fag" and "Retard".

Dipper was always going to have a hard time in high school, he had retrospectively accepted this. If his weird birth mark wouldn't have gotten him enough shit, his awkward demeanor and early voice break would have done it. 'But I could have lived with it,' he thought as he stared at those four ugly letters, 'I really could have. But no. I had to open my big fucking mouth and—'

"Is that him?"

Dipper became aware of two girls from his Biology class walking past him. He didn't bother turning around.

"It is!" The other replied quietly, not so quietly that Dipper couldn't hear her.

"It's the nerd that saves the world from a talking Dorito!" They giggled and continued down the hall.

Dipper hung in the corridor, his chest tightening and his blood boiling.

"He was a pyramid," he muttered under his breath before pounding his locker with a heavy fist. He flung his bag over his shoulder and stormed to the school's entrance.

"Uh oh, Dipshit's spazzing out again," muttered a student as he went. He quickened his pace.

"I'm going to do it." Dipper's voice was high and flustered. Mabel liked seeing him like this, though she could never really figure out why. "I'm actually going to fucking do it."

"So do it dumb-dumb! You said you were going to so just do it!" Mabel replied offhandedly, voice as chipper as ever.

Dipper hadn't been surprised to see her lounging on his bed and fleeing from the school. All in all, her attendance record was as bad as his, she just chose to skip the emotional stomping off and never go in the first place.

"I should've gone with Stan, both of them. When I think about what we could be doing right now I just... urgh!" He threw his arms in the air and flopped on the bed next to his twin.

"Coulda-shoulda-woulda!" Mabel replied, "You think you've got it bad? Jim hasn't texted me for two weeks!"

Dipper dragged a pillow over his face. "Jim Mavis just wanted you to fuck him." He sighed heavily into his pillow. "And you did, so now he's done with you. Just like how Mark is done with you. And Kyle. And Justin."

There was a time when Mabel's way with the boys worried Dipper, but at this point it was just another day to day hassle he no longer had the energy to put up with.

"You don't have to remind me," she responded, putting on her indignant pouty voice.

"I could go on."

"Don't." She gave him a light tap in the arm, giggling a little.

They lay there for a while in silence. They both inwardly reflected on their lives and how they had not developed the way they hoped.

"Maybe I haven't met the right man yet," Mabel eventually whispered. "Or... maybe I've known him my whole life..." Her hand travelled up Dipper's leg.

"Fucking STOP!" Dipper flung the pillow from his face, shoving it over his crotch. His face was red and frustrated. Mabel had always been like this, ever since they were young, but the years had made her braver. "It's sick, how many times do I have to tell you before it sinks in?" He spat at her, furious that he had to go over this all over again.

"Oh, and shooting up a school isn't, Dipper?" Mabel retorted, eyes fixed deeply onto his "You're soooo well-adjusted, aren't you? Perfect Dipper, the better twin!"

Dipper moved to the edge of the bed and buried his face in his hands.

"I'm not doing this today. Not today. I haven't got the energy, Mabel." He thought again about his locker, about the girls, about the hell that had been the last five years. He felt wet tears on his burning palms as he choked on his sobs.

Mabel touched his shoulders lightly from behind. Seeing Dipper like this upset her, yet at the same time she felt exhilarated. She eased her soft, thin fingers into his tense shoulders.

"You said you were going to do it, so why not just do it?" She whispered gently into his ear. "Why don't you?" She paused, listening to his stilted breathing. "Why don't you?" She repeated, almost too quiet to hear.

"Mabel, it's wrong," he managed to get out, voice and body shaking.

"Is it? Is it really?" She moved her hands from his shoulders and wrapped her arms around his body. "They'd be dead or worse if you hadn't stopped Bill. You're a hero and this is how they repay you?"

Dipper cursed himself, he could feel an animal inside of him agreeing to what she was saying.

"You're just taking back what you gave to them Dipper." Mabel bit down of his ear softly. "I'll even help you. You won't he alone. You're never alone with me." She moved her head down and started passionately kissing his neck. "Do it Dipper," her voice was rising now, almost hysterical. "Just fucking do it."

That night Dipper slept with his sister. It was the first and last time he had ever had sex, and though it disgusted him, he found that he had lost the energy to fight back—Against Mabel, against his inner demons. He was just tired.

"A-ah..." Mabel's breathing was heavy and labored as thrust herself upon Dipper's cock over and over again. "I-I...ah...I love you Dipper."

He never once opened his eyes. He lay there, still as the Gravity Falls lake. His mind took him back there. A place that was eternally summer, a world that was happy, a time that was innocent; a woman appeared before his mind's eye, she had red hair and freckles and a smile that was brighter than the sun, and though he couldn't remember her name, seeing her brought him peace. Staring deep into him, she opened her mouth and spoke to him:

"I love you Dipper."

Stan Pines was having a brief stay over in Antarctica when he read in his newspaper about yet another national tragedy.

Twins had gone into their high school and shot 14 dead between them. 8 more were injured. At the end of the massacre they had turned their guns on themselves, and ended each other before the police could have apprehended them and ask why they had done such a monstrous thing.

Stan then read the names of the twins.

And he wept.