You're a hacker when a hacker calls you a hacker. All that "being able to self-identify" is narcissism.
I would say that when the community calls you a hacker, then you are hacker. It's a title that others would want to give you and doesn't really mean anything other than the fact that you're generally good with computers.
Persuading this or any other title, although we do it all the time, it's stupid.
ps. The first guy that comes to mind, when I hear the word, is Linus Torvalds.
Hackers have called me a hacker, therefore I'm a hacker. I now declare that every human being is a hacker if they self-identify as one.