Complaint to the violator privately, or contact the moderator instead. I ask that people try not to take insult. Any complaints should be totally polite, respectful, emotionless, and non-accusatory, with no 'namecalling' whatsoever. Often this is impossible to do. When a flamewar breaks out, people usually blame a particular person for causing it, and they feel justified in responding.
Few people can be happy unless they hate some other person, nation or creed.
The test of a first-rate intelligence is the ability to hold two opposed ideas in mind at the same time and still retain the ability to function. If you really make them think, they'll hate you.