It could also be a feeling of empowerment, like, the retail worker can't retaliate to the treatment so the customer feels more able to act as they please?
I do believe you've hit the nail on the head. Same goes for when patrons are so shitty to serving staffing a restaurant. People sure are dick heads. I always hoped I would run across one of those folks stranded on the side of the road...could I leave them or not??
The sad fact for some is that because they get pushed around (by co-workers, boss, partner etc.) that they feel entitled to do the same to others for a momentary sense of empowerment. Of course, that moment is fleeting. It doesn't speak very highly of a person who acts in such ways.
I reckon, should you come across them, leave them...but then, at that point they might be polite and defferential. It's a hard one. Do we want to sink to their level or be the people we are naturally? Hmm. 🤔