If I observe a stranger treating someone in the service industry with any degree of elitism or condescension, I pretty much write them off immediately.
I came here to pretty much say this. Verbally abusing or harassing those in the service industry in any way will instantly lower my opinion of a person.
It definitely really disappoints me, especially when someone I know does it. It just seems like a complete lack of acknowledgement of the person as a person. Like in the moment and in the position they're in, they stop realizing that the person that they're talking to actually is alive with feelings and thoughts just like them.