1234, Main Street
Boston, MA 02123
<Recipient Address Goes Here>
<time you experienced bad service> <people receiving rude service> <description>. Unfortunately, we were treated very rudely by <employee(s)>.
This kind of behavior is inexcusable, and an unpleasant surprise from a company like <company name>. I would like <your suggestion>, but you do whatever you feel is necessary. Keep in mind, however, that your actions will demonstrate how much you value my continued business.
Thank you for your time.
encl: <List of enclosed items goes here>