Black people should have more respect for themselves than to use either form of the word, especially if they don't want anyone else using it. It's derogatory no matter how you say it, or who says it. The teacher was an idiot. He opened himself up to potential trouble, and anybody could have seen it coming. His rationale was stupid also. Who says he has to lower his standards because the students around him use those words? Hmm, aren't teachers supposed to be an example instead of conforming to the childish behavior of their students?