You should have stopped to think about why such a person was hired in the first place, while there are an endless supply of very talented, hard working, and honest young people who would never be given a chance at all.
But if I guess right, hiring is not seen as the responsibility of your company. And that's the core of the problem.
The hiring process is probably barely better than random, and, probably even closer to random for a junior hire.
Junior hires mostly don't know anything. So, you're pretty much hiring on "seems smart, curious, and enthusiastic" and praying a lot that you can train them. You're simply going to get misses.
This is one of the advantages that you get running "cooperative engineering" programs. You get to vet juniors before they get welded into your pipelines.
This kid would not accept seniority, would constantly and publicly try to divert from the stack we worked with, he would not take any input on his work without actively fighting the process and will crowd the conversation at team meetings with never-ending Reddit-tier takes that contributed to nothing other than fill his ego.
In the end I managed to convince my boss to get him out, and he now works in Cyber, which will probably cause even more damage in the long run, but at least I can now say "not my problem".