We hired a dev that's very much like you described. We "knew" he was smart because he did well in some Hackathons. Had built some cool projects on his flashy portfolio. Went to the same university we want to, which is a top university in the world. Had good grades at said University. etc.

He had all the markings of being a fantastic intern for us.

About half way through his internship we had to fire him. He lacked the attention span for a long term, rigorous software development project. We later hired someone whom we evaluated very differently and it has been incredible. He's doing a fantastic job. Constantly questions our opinions about software and pushes the boundaries of our depth of understanding.

To add to this, we knew the fired intern went on to another startup to keep doing whatever it is he thinks he's doing. The founders of that company ended up telling us the same exact problems were happening with them. Don't worry about these "hackers" and what they're doing. They'll all end up getting a reality check at some point. If they frustrate you, then just remember that the best revenge is living well.