The U.S. Supreme Court ruled in Chaplinsky v. New Hampshire (1942) that fighting words are not protected by the First Amendment. Fighting words are defined as words “which by their very utterance inflict injury or tend to incite an immediate breach of the peace.” As the Supreme Court explained in Chaplinsky, “[s]uch utterances are no essential part of any exposition of ideas, and are of such slight social value as a step to truth that any benefit that may be derived from them is clearly outweighed by the social interest in order and morality.”
However, the Supreme Court has significantly narrowed the definition of fighting words over time. And, it is important to keep in mind that even if speech is offensive, it is not fighting words if it is not directed at someone face to face.