This says much about respect and social competence in this society when the first instinct is to mock and abuse someone with different priorities than yours.

When they are that rude and stupid they have it coming

You mean “rude” in asking for a cashier? Not sure I understand

You mean demanding special attention rather than using the self-checkout like everyone else? Not sure I understand.

I expect that the management is responsible for adequate staffing. Self-checkout typically doesn’t even work. Not a boomer, not USian, YMMV.

Self checkouts don’t work where you are? Odd.

Typically they need attendant attention, to be reset to be usable. Which makes it rather pointless. My expectation that checkout lines are to be adequately staffed with cashiers. This is, however, increasingly not a safe assumption, in Germany. I expect the situation to further deteriorate. As does everything else.