Within an iphone app can you delete a user permanently?

When making an iphone app, and you need to ban a user, is it possible to ban them permanently? Like via their iPhone ID or something like that?
There's a person that is making an app and one of his problems is that he can't really ban anyone, he says, because they can easily make a new account.

See, the problem with banning a UDID or MAC address is that jailbreakers can easily change these things. If the app works by connecting to a server, you could try blacklisting IP's, stopping them from connecting to the server, and blocking common proxy IP's to stop the person(s) from using proxies to connect (though this will not work if it is a local app). Another way would be to blacklist an itunes account, so that if someone signs into their Itunes account in the app (like through gamecenter or IAP) then the app will make itself unusable (works with local and server). There aren't really very many ways to ban someone's IPhone, however, but those are some possible ways to ban someone who isn't jailbroken/very bright.