One reason could be a misunderstanding. Maybe someone in the pack misinterprets Stiles' actions as being against the pack's interests. For example, if he's involved in something that looks like it's endangering the pack but in reality he's trying to protect it.
It could be Vegeta. Vegeta might kick Goku out of a training session because he feels Goku is showing off or not taking the training seriously enough. Vegeta has always been competitive with Goku and this could be his way of asserting his dominance.
One reason could be if he was wrongly accused of stealing something important from the camp. Maybe a powerful magical item goes missing and Percy is the prime suspect because of his past issues with authority. Another reason might be if he accidentally endangers the camp in some way during a mission or training exercise. For example, if he unknowingly leads some dangerous monsters back to the camp.
Stiles might be initially shocked. He would probably feel betrayed since he thought of the pack as his family. He could go into a state of denial at first, not believing that they would actually kick him out.
One possible reason could be that he's framed for a crime he didn't commit. Maybe someone planted false evidence to make it seem like he was endangering the guild. Another reason might be that his power got out of control and the guild, fearing for the safety of its members, made the tough decision to kick him out.
It's hard to say exactly. It could be related to a dare, a competition gone awry, or even a misunderstanding among friends. Maybe the guy being lifted moved unexpectedly, causing the lifter to lose their grip.
He might be really angry at first. Natsu is a passionate character, and being kicked out unjustly would make him furious. He could storm off vowing to prove his worth and show the guild they made a mistake.
Percy could also be very sad. He has so many memories and relationships at the camp. He might go into a state of depression for a while, not knowing where to go or what to do next. But then, he would probably start to think about how to get back in or how to make things right. He might start looking for evidence to clear his name if he was wrongly accused. He could also look for new allies outside of the camp who could help him in his situation.
Naruto might initially be shocked and hurt. After all, being expelled by his own family is a huge blow. But being 'godlike', he could quickly turn that pain into determination. He might decide to prove his worth and show his family that they made a big mistake.
Xander could be a creator or an owner. Maybe he is the person behind a brand, a story, or a platform. And he kicked out fanfiction because he wants to protect his original creation from being overshadowed or misinterpreted by fan - made stories. It's also possible that Xander is a figure within a community who has a particular vision for the content that should be present, and fanfiction didn't fit into that vision.