I think my boss should ask a regular customer not to return
What is the point in asking this customer not to return?
It's because this regular customer treats us like we work for free.
It is not very professional to try and get your boss to ask a customer not to come back. If you feel the customer is disrespecting you then it makes sense to bring this up to your boss, and let them decide how to proceed. It sounds like your goal is just to harm the customer, and that is wrong.
Fine...
I hope that you are able to bring this up with your boss, and that the problem can be solved.  If this customer is indeed being too demanding, then the manager might be able to set firm limits on what can and can not be offered.