How you use your voice initially is want is most important, be very calm but strong. There are many reasons for improper behaviour by guests and sometimes we can see them coming. We have a series of Service Excellence programs that can help you and your employees turn this situation around. If you dont ask a customer like that to please leave the store you will loose respect from not only your staff but also your customers because you just lost control of your room. There is a certain point of no return and it sounds like it was out of hand from the start so at that point you become a fool at his game.
Angry people prey upon the overly kind.
While never raising my voice, I use direct eye contact and, while trying to get to the bottom of the situation, always remain calm. If the customer is right, I take steps to address the problem. I have no problem asking people to leave. I have actually gotten repeat business from witnesses by actively sticking up for staff. Sometimes a change of server will do the trick.