Perhaps Peter failed to follow Tony's instructions regarding some important technology or protocol. Tony, being a perfectionist and concerned about safety, would then yell at Peter for not listening. In the fanfiction world, this kind of conflict adds drama and tension to their relationship.
There could be a strain in their relationship. Peter might feel hurt and start to distance himself from Tony for a while. However, this could also lead to a deeper understanding between them as they later communicate about their feelings.
Perhaps in the fanfic's storyline, Tony is facing a lot of pressure himself, like threats from powerful villains or issues within the Avengers. Peter's actions, whether they are mistakes or just inconvenient timing, could be the straw that breaks the camel's back for Tony, causing him to yell at Peter.
One possible reason could be a disagreement over superhero tactics. Peter, being young and idealistic, might yell at Tony if he thought Tony's methods were too extreme or not in line with his own sense of justice. For example, if Tony made a decision during a battle that put civilians at risk, Peter would likely be very vocal about it.
Peter might be initially shocked and a bit scared. After all, Tony is like a mentor to him. But then he could become defensive, trying to explain his actions or point of view.
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.
Maybe Peter misses an important training session. Tony has probably put a lot of effort into training Peter to be a better superhero. If Peter skips out on training for something unimportant, like going to a party or just being lazy, Tony would be justifiably angry and yell at him for not taking his superhero responsibilities seriously.
Maybe Peter inherits Tony's high - tech gadgets. For example, he could get access to some of Tony's Iron Man tech, which would be a huge deal. This could set him on a new path in his superhero journey, perhaps allowing him to upgrade his own suit or develop new abilities.
The fanfiction could also focus on the emotional bond between them. Maybe Peter gets into a dangerous situation and Tony has to face his worst fears of losing his son. This could lead to a deeper understanding of their relationship and how they rely on each other not just as superhero partners but as father and son.
In the fanfiction world, there could be a prophecy or a pre - determined fate that Tony believes in. He may think that Peter's sacrifice is necessary to fulfill this prophecy and save the world from some greater threat related to the Soyl Stone. He might see it as a selfless act in the long run, even though it seems cruel.
Well, it could be that in the fanfiction, they argue about technology. Peter, being the brilliant young mind that he is, might have different ideas on how to use or develop Stark tech compared to Tony. Tony is more experienced and perhaps set in his ways, so when Peter challenges him, an argument ensues.