Appocolyptic, the dictionary has nothing to do with it. Your reasoning is irrational. The word nigga/nigger has a derogatory connotation. You are incorrect to assume that all black people are "cool" with hispanics using nigga, or that all black people are "uncool" with white people using nigga in a "friendly" context. Regardless of which black people think what, the fact of the matter is that a word with such hateful origins cannot be used in a friendly context by white people in some black people's minds. That's it. Respect that and move on with your life.