The doctrine comes from Chaplinsky v. New Hampshire (1942), where the Supreme Court held that certain speech falls outside constitutional protection because it's not essential to any exposition of ideas and has low social value compared to the harm it causes. Fighting words were defined as words that by their very utterance inflict injury or tend to incite an immediate breach of the peace — essentially, insults directed at a specific person likely to provoke a violent reaction on the spot.
The category has been narrowed heavily in practice since 1942. The Court has never upheld another fighting-words conviction, and cases like Cohen v. California (1971, the "F*** the Draft" jacket case) and Gooding v. Wilson (1972) struck down convictions for speech that offended but didn't target a specific individual with an imminent threat of violence. Courts have also rejected the idea that words merely because they're racist, sexist, or otherwise deeply offensive count as fighting words — the doctrine requires a face-to-face, direct provocation likely to trigger immediate violence, not just offensive content.
I do not believe that telling off an 8 year old kid would likely be a direct provocation likely to trigger immediate violence.
Yes, as I said, I thought her defense against a "fighting words" charge would be strong, but I also said to FLT-Bird that a law exempting "fighting words" from Amendment I protection was NOT unconstitutional.
By the way, I think the Fuck the Draft decision was wrongly decided.