One possible reason could be a misunderstanding. Maybe Peter accidentally gets involved in something that looks bad to the Avengers, like being in the wrong place at the wrong time during a security breach. So they misjudge him and are mean as a result.
Perhaps there's a difference in ideology. Peter has his own way of doing things, which is influenced by his youth and his experiences in Queens. The Avengers, with their more global and experienced perspective, might not agree with his methods and this leads to them being mean to him. For example, Peter might be more focused on helping the little guy on a street - level, while the Avengers are thinking about bigger, world - saving plans.
It might be due to jealousy. Peter is young and has a lot of potential. Some of the Avengers, who have been around for a while, could feel threatened by his quick rise and popularity. So they act mean to try and hold him back or put him in his place.
He might also get angry. Peter has a strong sense of justice. If he feels that the Avengers are being unfair, he could stand up to them. He'll use his quick wit and his powers to show that he's not going to be pushed around easily.
One possible reason is that Peter's quick rise to popularity among the public might make the Avengers jealous. They've been around for a long time, and suddenly this young kid is getting all the attention.
One possible reason could be jealousy. Maybe Peter has some natural talent or ability that Tony wishes he had, and this makes him mean. For example, if Peter is really good at something like coming up with innovative ideas quickly, and Tony, who is used to being the smartest in the room, feels threatened.
In some fanfictions, Peter could have a secret that he's keeping from the Avengers. When it's eventually revealed, they might feel betrayed and turn against him. It could be something related to his powers, or his past associations that the Avengers find unacceptable, thus resulting in their hatred.
One possible reason could be overexertion. Peter Parker is often in high - stress situations in the Avengers. If he uses his powers too much, like constantly swinging around the city or fighting powerful enemies without proper rest, his body might give out and he could collapse. Another reason might be some sort of poisoning. Maybe he gets exposed to a new kind of chemical or toxin during a mission that affects his superhuman physiology.
It could also be due to jealousy. Peter might be getting too much attention from the public or other superheroes. His youth and new - found popularity could make the more established Avengers feel overshadowed, leading to feelings of resentment towards him.
It could be that Peter's immaturity showed in a crucial situation. He might have been over - confident and tried something really risky without thinking it through. The Avengers, being more experienced, would be frustrated with his recklessness and thus yell at him. They want him to learn and grow, but his actions might have been too much to tolerate at that moment.
Well, it could be his age. Peter is relatively young compared to the other Avengers. They might assume that a young person in their highly - secure area is an intruder. Also, if he showed up at a time when they were on high alert, like after some threat or security breach, they'd be more likely to suspect him. For example, if there had been a break - in attempt recently, and then Peter just swings in out of nowhere.
One possible reason could be that Peter is being framed for something. Maybe there's a misunderstanding where evidence is planted to make it seem like he's betrayed the Avengers, so he flees to clear his name.
Differences in ideology can also play a part. Tony might have some views on how to handle threats or use technology that the other Avengers don't agree with. Maybe he's more willing to take risks with untested tech that could endanger the team or civilians, which would lead to resentment.