There is, put simply, only one book I would demand a community manager has read. It was first published in 1937 and has sold almost 17m copies worldwide.
There simply isn’t a better book out there about how to handle diverse and difficult people.
If you haven’t read it yet, I suggest you make it your new year’s resolution to do so.
Bonus: You can read the summary on Wikipedia, but this doesn’t nearly do the book justice.