Yes, but nothing happens. Totally same thing that you have right now someone knocking using ssh, bots etc.
If you set up such site/forum then yes they would send visitors who would see what ever you started using that domain. But they can’t hijack your domain, because you are telling to world wich nameserver that domain uses and to what IP it is pointing. And there is web server letting visitors in, if they are requesting such site you are configured for that domain. If request domain doesn’t get anything then doors stay closed.