I've mentioned this before (e.g. Lowest Common Denominator) but between the years of 2009 and 2013, I talked to something like 13,000 to 15,000 people while I was doing retail and SMB sales for Verizon. I learned a lot from that period, but one of the things I learned that I did not expect was what I now call my "5% rule."
No matter how kind, warm, thoughtful, amazing, cheerful, consistent, and perfect I treated people roughly 5% of them would just be terrible (yes, I have the numbers to back this). I'm not talking about people who were having a bad day or people who were trying to work the system. There was a legit 3% to 5% of people that just wanted to be mean, nasty, selfish brutes. People that were unpleasant to be around. People who for one reason or another "wanted the world to burn" ( in the words of Christopher Nolan).
I know what you're thinking: "sure buddy... you were doing sales and you're blaming the customer for being nasty...never heard that before." The thing is... this number has held up in other parts of my life too (dating, restaurant customers, etc). And if you ask anyone who has done big numbers working with people they'll say the same thing (my doctor friends specifically would say I'm being generous).
I went on many many fewer dates than sales calls but pretty much the number was something around 3%-5% where the women were just terrible - like only going out to get a free meal and drinks, or bigots, or were completely self-absorbed, or just generally nasty people.
My experience serving/bartending in restaurants was the same... As an example: one time a lady threw a huge fit about a 2-3 inch smooth brown hair being in her meal when her server was a blond girl and the entire kitchen staff were 35+ year-old Mexicans/ African Americans with completely shaved heads. Now I'm not saying this woman brought the hair into the restaurant and planted it in her meal... but I know for a fact it couldn't have been from any of our staff in the restaurant, so you can make your own decision.
Of course, the optimistic take here is: Wow! 95% of people are nice, kind, wonderful human beings...
Sorry. No. That's not the take here. 3% to 5% of people for whatever reason just plain suck.
The optimistic take is that if 3%-5% of people just suck, you really have permission to free your mind of those people and just focus on taking care of the people who don't suck. Just expect it and move about your day.
Is this customer terrible because they need help, and empathy, and are having a bad day? Probably. The 95% probability says YES. It says that you should bring your best self to those people and try hard to make their lives a little better.
However, if for some reason a person comes into your store, pulls down their pants pisses on your merchandise, and claims that they are doing this because Motley Crue used to do it before shows at the Whiskey a Go Go... that's the 5% rule and you should just call the cops and let that moment go - it has NOTHING to do with you. You didn't create, enable, or plan for them... nor could you. They are just part of the 5% of people in this world that suck. Eventually, they'll get some come-up-ens but often enough, you just need to let the moment pass.