Answer:
If the said customer is being violent, you should alert the authorities, or if one of their friends/relatives is there to give the customer a ride home, allow that to occur as soon as possible.
A second thing to do if a person has had enough drinks is NOT to serve any more alcoholic beverages, nor let any other person buy any beverages for them as well.
If you follow number 2, the likelihood of alcohol poisoning decreases substantially. If you follow number 1, the likelihood of said customer arriving home safely increases substantially.