For a more extensive article on the theoretical side of body pressure, check out my post Space Invaders: How Humans Pressure Dogs and Other Animals. 

So you are standing at a party, or in your office, or on your front lawn. Someone you know only vaguely walks up to you. He walks up very close, face to face, close enough that you can see up his nose and smell his breath. He starts a conversation. What do you do?