Being a Grammar Nazi doesn't make you a good admin. If I were appointed admin, I would quit my Grammar Nazism right away.
The ones that need banning are the ones that consistently stir up trouble without remorse, the ones who spam shamelessly (posting things that cannot be humanly understood counts as spamming in my head), and the ones who fail to follow the rules regardless of how many warnings they get (repeatedly necro-posting, asking for Ultima Edition help, etc.).
Not that I'd make a good admin. I'm terrible at knowing when to assert myself and how.