Obscenities are not protected free speech under the Constitution of the United States. The Supreme Court made that clear in 1957. What has remained less clear since then is just what can be considered obscene and thus illegal.
Back in the day, the rules of etiquette required that if you got into a fight in the schoolyard and a teacher broke things up, you would shake hands with your rival. An apology might even be called for. Does that ever happen anymore?