The customer is not always right...and don't argue with the worker about what we do and don't do...you don't work here. Okay?

Okay with me.

"The customer is not always right...": the mantra of a business that's about to fail in a competitive world.

That person trying to point out the error of your ways may have done your job in the past and actually knows the score. I've run into that at supermarkets with people packing my groceries. Sorry, the bread and eggs go on the top, not the bottom, don't care how many other bags you've packed the wrong way.

It's true, the customer is not always right. Sometimes they're anal-retentive jerks and no amount of kindness will appease them. You have to learn how to deal with them though, it's part of the deal.

I suggest you just be a nice as possible, grin and bear it until they're gone. One plus to this is other people will notice their rudeness... which leads to some pleasant surprises. Sometimes...

If you were not black, I would swear you are AG.  Are you sure you are not AG?   Do you work at Subway?