There is -- or should be -- no line. Not in law. If one wants to object to someone else's expression in some non-physically-aggressive manner (in the libertarian sense) then they are welcome to do so on the principle of equal liberty. Congress shall make NO law abridging the freedom of expression. All the supposed exceptions to free-speech absolutism are equivocations that attempt to make legitimately outlawing physical force accompanied by some form of epiphenomenal expression equivalent to legitimately outlawing expression. Hurting someone's feelings or offending their sense of propriety is not harming them in any way they cannot avoid by merely discounting the offending expression. This is all so obvious that it is only the totalitarian mentality that can refuse to see it. Such a mentality does so for obvious reasons: Without thought control there can be no suppression of the individuality that demands personal sovereignty -- the death knell of all forms of collectivism.