I'm not a nice man, but I'm a good man. Being nice, in my perspective, is speaking or acting in a way contrary to how you speak or feel (ever heard the phrase "just being nice"?). I don't bullsh*t people; I say what I feel and when I say something complementary, you don't have to wonder if I'm saying it just to make you feel better.
Not that I make it a point to hurt people's feelings, not being nice is not the same as being mean. If I don't like someone, I can just as easily ignore them as insult them. As a matter of fact, those that know me understand that the best way to tell I don't care for someone I'll be the epitome of politeness towards them. Joking around and insulting is for friends who know the spirit it's done in and will give back just as good.