A guy who sent me ?150 for "wasting my time" because I didn't do CIM sent me an awful one as I didn't thank him profusely (I wrote something along the lines of "I really hope you find the regular girl you're looking for yadayadayada) but was away with a client and had a limited time each day to answer the ungodly number of - mostly stupid - emails I receive, as well as contacting friends and family. It was so vitriolic I cried, partly because I felt guilty! When you put so much effort into being courteous and efficient, it's really quite cutting to be accused of being the opposite.
In the words of Frozen, you just have to "let it gooooo!"