Just as the First Amendment doesn't allow you to spur others to illegal or lawless actions, it doesn't protect you from uttering "fighting words." Fighting words are insults you hurl at another person in face-to-face conversation, which are likely to immediately start a fight. The U.S. Supreme Court came up with the "fighting words" doctrine in 1942 in Chaplinsky v. New Hampshire.
Walter Chaplinsky, a Jehovah's Witness, was distributing religious literature in New Hampshire in 1940. A group of people didn't appreciate it when he called other religions "a racket," and mobbed him. The police stepped in, ushering Chaplinsky to the police station for protection. But when he got there, Chaplinsky berated the city marshal, allegedly calling him "a goddamned racketeer" and "a damned Fascist." The marshal promptly arrested him for breach of peace, and a jury later convicted him in superior court [source: Hudson Jr.].
Chaplinsky appealed his conviction all the way up to the U.S. Supreme Court, but lost. The Court agreed with the New Hampshire Supreme Court's ruling, which called Chaplinsky's language "dangerous words." U.S. Supreme Court Justice Frank Murphy wrote in the Court decision, "There are certain well-defined and narrowly limited classes of speech, the prevention and punishment of which have never been thought to raise any Constitutional problem. These include ... the insulting or 'fighting' words — those which by their utterance inflict injury or tend to incite an immediate breach of the peace" [source: Hudson Jr.]
Although the Court never overturned the Chaplinsky decision, First Amendment scholars often categorize it as a troubling one, in part because many state courts use it to uphold the convictions of those who criticize the police.