In some interpretations, Sherlock could be a bit hurt by it, although he would never show it outwardly. He might retreat into his mind palace for a moment to collect himself and then come back with a sharp retort. This could also lead to some character development where he starts to question how he is perceived by others and whether he should make an effort to change that perception.
He might be initially shocked. Sherlock is used to John being more understanding, so this outburst could catch him off - guard. But then he could go into his logical mode and start analyzing why John would say such a thing.
His extraordinary intelligence could be one reason. People who don't understand his quick deductions and unique way of thinking might label him a freak. For example, his ability to notice the smallest details that others miss can seem abnormal to the average person.
She might get angry and defensive. In many fanfictions, characters don't like to be insulted. So, Bella could lash out at the person who called her a brat, demanding an explanation.
Sherlock might initially seem unperturbed, which could annoy Moriarty. He'd use his sharp mind to analyze Moriarty's motives and actions. He could also try to engage Moriarty in conversation to gain more information. He might say things that would make Moriarty second - guess his own plans. For example, he could point out flaws in Moriarty's previous schemes, making Moriarty angry or distracted. This would give Sherlock an opportunity to either escape or plan his next move.
Sherlock would be extremely worried. He might go into a state of hyper - focus, using all his skills to find John. He would analyze every little detail, from the place where John was kidnapped to any possible witnesses.
Sherlock might also feel a sense of responsibility, even if the pregnancy wasn't his doing. Given his loyalty to his friends, he would probably try to be there for Molly. He could use his connections to ensure she has the best medical care available. And in the long run, this could be a turning point in his relationship with Molly, either bringing them closer together or causing some strain depending on how he handles the situation.
Maybe John was frustrated at Sherlock's eccentric behavior. Sherlock often acts in ways that are outside of normal social norms, like his extreme focus on cases and disregard for basic social niceties. This could have led John to lash out and call him a 'freak' in a moment of exasperation.
Well, the Avengers are a diverse group. Hawkeye might just shrug it off as something he doesn't really care about. But Iron Man would likely be drawn to the technological aspects that might be added in some fanfictions. Captain America would be more interested in the moral and ethical elements that could be explored in the stories. Black Widow would be observant, noticing the different characterizations and how they deviate from the original Sherlock Holmes. And Thor would probably be the most out - of - place, trying to make sense of this strange new form of storytelling.
In many Sherlock fan fictions, Sherlock branding John could be a sign of his trust or a way to get a reaction out of him. It all depends on the author's imagination and the context they create.
One possible fanfiction could be 'The Unforeseen Danger'. In this story, Sherlock and John are on a case chasing a serial killer. While investigating an abandoned building, they are ambushed. John gets stabbed while trying to protect Sherlock, and Sherlock, in his rage to save John, gets a severe blow to the head. But their strong bond helps them get through the ordeal.