John sits down at the breakfast table one morning and says to Sherlock, "In this fanfiction, I would like to engage in sexual intercourse with you."
Sherlock puts down his tea and nods. "Definitely," he says. "It would be excellent representation for the queer community, which is the only valid reason to depict a romantic relationship between two people of the same sex."
"Of course!" says John. "Anything else would be fetishizing."
Sherlock smiles, because he is very happy. "I am very happy," he says. "Let's have an extensive discussion about how to have the sex we want to do, now that we have ascertained that there is mutual consent."
"We will need to purchase condoms," says John.
"Must we?" Sherlock asks. "After all, we are unlikely to become pregnant, and we can both prove that we are clean of any sexually transmitted infections."
"Of course!" John says, taken aback that Sherlock would ever question the inviolable laws of fictional coitus. "If we fictional characters do not use condoms for every single sexual encounter, then underage consumers might not learn the importance of using protection."
"Underage consumers of adult content?" says Sherlock, somewhat taken aback.
"Don't kinkshame the teenagers," John says sternly. "It's fanfiction's responsibility to deliver quality sexual education to youth. We must be role models."
Somewhat chastened, Sherlock nods. "I apologize. I am five years younger than you, so I do not know all these things."
John's eyes go wide. "You're younger than me?" he says, his voice hushed.
Suddenly, there is a knock on the door. "Police," calls a voice.
"You can just use your name, Lestrade," says Sherlock.
Greg Lestrade kicks in the door, which is a metaphor for police violence and also assault. "John, I'm arresting you for pedophilia."
John hangs his head. "I knew you would have to."
Lestrade wags a finger. "Sherlock is five years younger than you," he scolds. "He's clearly minor-coded. And he's sexually inexperienced as well. And I'm to understand that you initiated this adult discussion with your adult flatmate? You sick fuck."
"Wait!" Sherlock jumps to his feet. "John is shorter than I am, and in the earlier portions of the television show, I was depicted as being the more dominant of the two of us! That makes John minor-coded and me the predator!"
Lestrade stares at the two of them for a long time. Gradually, the stance of his body shifts as his arms hang limp at his sides, fingers twitching occasionally, as if synapses were attempting to fire. His eyes go glassy and blank, the pupils dilating until they drown out the brown of his irises.
"I," he says. "I…" A thin stream of blood trickles down from his nose, and then he collapses on the floor of the living room.
John goes over and takes his pulse. "His brain shut down from trying to understand who was being exploited," he said.
Then the entire fanfiction was deleted from the internet and the author arrested, because she was secretly a filthy fujoshi who was writing slash not even to provide representation for queer people, but to get her rocks off. And she was still writing fanfic at 28, which is well past the acceptable age for anyone to be in fandom. Go knit a tea cozy or something, you toothless hag.