Dear Customer:

Just a helpful reminder that we are human beings too. No, we're not perfect, and we make mistakes too. And while that may inconvenience you, we do apologize for that, and we don't treat you like dirt when you make mistakes (which you do, because like us, you're human). Also, please keep in mind that while we do make mistakes, keeping calm and working with us instead of getting angry and blaming us will actually make things go faster, believe it or not. And just because it's easier for you to take it out on us and blame us for something that may not even be our fault, doesn't mean you should.
Remember, we are here to serve you, but we're not your servants.

(P.S.: There is no need to give us dirty looks when we inform you of a policy. There are certain things we cannot do, and doing some of these things will cost us our jobs.)

Thank you
-Everyone Who Works in Customer Service