Within reason, if you piss someone off, for whatever reason, they should be allowed to express their input on you, no matter how explicit that judgement may be. That's one of the features of this reputation system. If we'd regulate what we can say in a reputation comment, it's like limiting our options on how we feel about someone, and that's just morbid.
Not all the time. Flaming shows the degree of dissatisfaction with the member. Even the most literate people, those that can express themselves impeccably without swearing or muttering a single cuss word often have slip-ups.
It's a personal opinion and we could go on for ages arguing about it.