Perhaps you mean libel and slander? In which case yes, the courts rule on those.
But insults? If you could sue for being insulted, the court system would grind to a complete halt.
Exactly, and if a court can decide whether something is libel or slander, it can just as easily decide if something is a pure insult, or blasphemy, or pornography. And historically, the courts have decided that and nothing ground to the halt.