When I was little and someone would do something to the family that couldn't be immediately rectified, my mom would say, "I may not be able to see it when it happens, but God will get them for that." The landlord that didn't raise the rent but refused to fix anything that broke ... check. The shade tree mechanic that "fixed" the car for all the money we had left only to have it break again a day later ... check. The big truck on the road that changed lanes without looking and caused us to go into a ditch (without checking on us) ... double check.
You may say that for two of the above examples, she should have pushed for the house repairs or taken the car back until he got it right. That wasn't her way of handling things. My father was an abusive husband. She was so beaten down for so long, that she was too afraid to push back until she was much older. To potentially anger the landlord might mean having the rent raised or being kicked out. To push too hard with the mechanic might mean the car would never be fixed, leaving her without a way to get to work.
I've shared her little phrase with people over the years, as a way to lighten the mood after an icky customer and to subtly remind my coworkers, without pushing my moral code on anyone, that these people will face repercussions for their behaviors. It's so much more depressing to imagine that those who treat service industry workers poorly will get away with it for the rest of their lives, have wonderful relationships and die happy & rich. I'm not wishing death and destruction on anyone, just an equalizing reaction.
Today, I dealt with a man that was very uncomfortable to help. It was clear from the moment he arrived that it was going to be a challenge to keep my composure. He was condescending, accusatory, argumentative and prepared to fight. His wife had visited a few days earlier, and I had suggested that we needed to make some corrections for her. The story she told me that day was completely different from the one she told this morning. It was clear that she had had to find a scapegoat in order to deflect his anger away from her. I could recognize her discomfort, her need to keep apologizing ... it was fairly clear that he kept her in line. I've lived that life, I know the signs.
In the end, I was thankfully able to accomplish what they wanted done, and adept enough to hide that I needed to partner with someone on how to fix the part I didn't understand. The main rule with the really bad customer is to get them out as quickly as you can. They spread dissension, make the other customers uncomfortable or nervous and wreck your sales. Move them off to the side, lower your voice so they follow suit, fix it fast if you can or promise to follow-up ... and then do it, so they don't come back.
This guy was so bad though, walking so close to the line, that I would have loved to refuse to help him - but you don't get to do that in customer service (except in rare circumstances). You just have to take it and then not take it personally. When it was all done, and the moment was right, I got to share mom's phrase with a new set of people, and spend a couple hours fantasizing about this guy's equalizing reaction.