Most of the time, our attitude to work is, "Better done than perfect." If you do more or less of what you're supposed to, nobody's gonna notice that a couple details aren't quite as good as they could be.
This is especially true when you're doing the bare minimum while dealing with a rude customer. Maybe they'd get better service if they weren't so rude, but they'll never know.
But unfortunately, if we always take this approach, we might end up in situations like these.