As a general rule of thumb, someone can say what they want, but if you enter my personal space, it is a done deal. At this point, it has escalated from sh**it talking to a physical confrontation. It's foolish to wait for the them to throw a punch, push you, grab you, or whatever else. Don't let them get the upper hand. Hit hard, first, and more often.
If someone is not fighting back, submits verbally, or is knocked out, it is over. If you continue beating them at that point you are looking at lawsuits and assault charges. You will still possibly be looking at those two things even if you stop.
In my "street" experience I can tell you it's not hard to determine who will attack and who will run their mouth. It also helps to know your environment, your surroundings, who is watching you, how many there are, that sort of thing. I'm sure those who have either worked in the bar scene or hung out in it a lot knows you can usually see a fight coming a few minutes before it happens, sometimes longer, if you are looking.
"The hero and the coward both feel the same thing, but the hero projects his fear onto his opponent while the coward runs. 'Fear'. It's the same thing, but it's what you do with it that matters". -Cus D'Amato