I just realized I come from a country where "don't be an asshole" is a common phrase that is considered harsh but not mean ;-)
In my circles, at least, 'don't be an asshole' and 'you are being an asshole' is harsh-not-mean, while 'you are an asshole' is mean-maybe-harsh. The explicit declaration of state of being, rather than observation of behavior is the differentiator.