Currently I behave because it's in my interest to abide by laws, even those I don't agree with. If all authority disappeared overnight, I believe my best course of action would be to immediately assemble an armed militia so we could enforce a set of rules within a community that we believe are the best. I would still respect many social norms, but definitely not all of them. One thing that comes to mind is that "innocent until proven guilty" goes out the window. If I perceive someone to be a threat then I will use whatever means I have to neutralize them, rather than waiting for some kind of arbitration.