I can explain at least part of it.
For workers who are talking mean about customers, well... let me put it this way: Spend just a short time in customer service, in cashiering, in any thing like that where you're directly involved with that basic interaction with customers at a high frequency and, well... sooner or later you will become just as jaded as they are. I dont work anymore, but from my experience back when I did, I know *exactly* why they get so judgmental about customers and such. Anyone working retail knows that customers as a whole are, honestly, pretty horrible. It's very hard NOT to have a super negative view of them. And sooner or later, you're gonna start to vent a bit.
It may happen less for those on the spectrum, but for most... yeah, it happens.
It's not that the workers are secretly awful people or something like that. It's that the nature of the job and frequent abuse from customers will eventually get them into that perpetually sour, angry state while on the job. But they *must* pretend to be super friendly even to someone who is screaming at them, or they get fired, and that just makes it even more infuriating.
It's just a natural response to the abuse and stress that comes with working retail. Or many other customer service positions.
If you dont want people talking nasty about you... always be polite with them. I guarantee you, that cashier you're working with is probably having a bad day (I know I always did... not even once did I *not* have a bad day when at work). Dont make it worse, and they wont think you're terrible.