Fighting words are words intentionally directed toward another person which are so venomous and full of malice as to cause the hearer to suffer emotional distress or incite him/her to immediately retaliate physically. Fighting words are not an excuse or defense for a retaliatory assault and battery. However, if they are so threatening as to cause apprehension, they can form the basis for a lawsuit for assault, even though the words alone don't constitute an assault.
The utterance of fighting words is not protected by the free speech protections of the First Amendment of the U.S. Constitution. The words are often evaluated not only by the words themselves, but the context in which they are spoken. Courts generally impose a requirement that the speaker intended to cuase a breach of the peace or incite the hearer to violence.