I tried with that one. I stumbled over myself, explaining that some people were never taught to be nice, or that perhaps no one was ever kind to them, or that maybe they were actually afraid and trying to psychically protect themselves or that possibly they didn't have a nap that day. What I should have done was look into his quizzical little face and tell him the truth: "Sweetie, I don't know." Because I can't actually teach him why some people are mean. What I can do is teach him that sometimes even parents don't have the answers. Sometimes we are all, even wise grown-ups who know about jelly beans and aerospace, left wondering, Why?