Unless and until that person actually commits a trespass, or there is clear evidence of an imminent act of trespass (having a gun pointed at you, for example, or pulling back to swing a fist at you), you don't have any ethical grounds to strike them.

The point isn't to achieve happiness. The point is to achieve peace. To not be aggressed against. Hitting people for words you find vile or cruel opens the door to others doing the same to you for words they consider vile or cruel, even if only they feel those words are. It maximizes conflicts.

We're not bears. We're not base animals that lack the ability to reason. It certainly may seem that way sometimes, and there will always be sociopaths, but humanity is distinguished from other animals by our ability to reason. I'm all for reciprocating garbage speech with ostracism and exclusion, but to argue that physical force is an ethically acceptable response to words allows the worst kind of thing: violence against people for unpopular speech, not just cruel or vile speech.