To touch on DefendThyself post.
You should have in place as a part of your training a way to judge distance and where the threat is in your circle of control.
You need to understand if you are in a circle of situational weakness or strength. (how much of a threat does the environment around you hold)
What are your options and understand the sooner you can break the circle of conflict the less the chance of damage or expansion problems.
There are many factors that must be in play before the circle of convergence is draw and a fight begins.
The key is becoming good at seeing the signs of trouble and moving clear. So to answer the question, "what to do if they are screaming in your face". Look around and judge the situation and clam down the mood and walk a way.
space is occuplied and distance is judged and always fight the circles not the man.
Maximum Combat: Finding the Power in Ancient Martial Arts Principles