Ooh, sorry to hear about the bad day

There will always be people like that sharing our air (sad, isn't it?) and I'm another who believes that what goes around comes around.
I was a hairdresser for a long time, and we'd get people like that, too. I don't know how a person could use 3/4 of a bottle of shampoo, then demand we refund the money because "it wasn't good". Well if it wasn't good, wouldn't you have figured it out within the first few tries? Uh, yeah. Then there were a few people who would do the same with conditioner, but DILUTE the leftover stuff with water! Like we wouldn't notice...
The best, though, were the people who came in for updos (prom season, military ball season, etc.). They knew up front what the cost would be, and after a stylist would work on the client's hair for 1 1/2 hours +, the client would try to get away with the "I hate it" excuse and not pay. One of the best updo people in the shop had this happen, and as soon as he heard about the no pay client (who was still at the front desk), he calmly walked up and quietly started taking the pins out of the 'do and letting it all fall. The girl was mortified. Let's just say that suddenly the hair was beautiful and she paid up. The entire salon decided that Le was the hero. LOL!
Keep your chin up, and remember that for every rotten jerk that comes through, there are 10 nice people who appreciate what you do