A couple of years ago, I had the chance to work on a project with a local news anchor. It involved several meetings with her. What struck me before, during and after these meetings was her behavior. Rather being a polite, gracious and a cooperative colleague, she was rude, constantly late and displayed "diva-ish" behavior. Instead of a local news anchor, it felt like we were working with a world touring singer. I found her behavior both annoying and silly. Because as a local celebrity she might be well known in her own town, but the moment she goes elsewhere, no one knows about her status and no one cares.
I find the same principle is applied to high school divas and divos (yes that's the actual word for men). They may have gotten cast as the lead in every show in high school, but the moment they go off to college or start auditioning professionally, they're right back to the same level as everyone else. Which is why I never accepted obnoxious behavior from them.
High school theatre is a time where you should learn as much you can both as an actor/designer/writer but also as a collaborator. Believe it or not, the teamwork skills you learn as a high school student are only going to help you in the long run.
Also, if you're displaying obnoxious and egotistical behavior now, the humbling nature of professional auditions is only going to hurt more. Students who think that it's going to be easy because they got every role they wanted in high school and quickly find out that's not going to be the case in a larger pond, often drop out or quit. Those who know it will be an uphill climb are more prepared for the amount of rejection before finally getting the gig.
So take the time in high school to soak everything in. Make connections with people that could help you down the road. Be a resource that can be relied on. Understand the roles you might be getting in your school will not be the ones you immediately get in college or professionally. Get ready to handle the rejection and appreciate the successes.
If you undertand this, you're going to have a much better time navigating through this industry.