The ruder the customer, the less English I understand.
I find this to be the most efficient method of making rudies leave.

Don't be too bothered.
If ever you should meet a person whose very presence curdles milk, remember this:
Despite our incessant need to enlarge our ego with the broken bits of our fellows and argue over every little thing, we do tend to share the same ideals, at least culturally. In other words, as humans, we have a sort of universal idea of likability in a person. With that being said, it is highly probable that everyone else this unpleasant person encounters shares the same opinion of him/her as you. Which increases the likelihood of said person getting punched in the face.