Here is a nicely turned piece by David Mitchell at the Observer (yes, it still exists) about manners.
I think they both sound horrible and they deserve one another. The more time people like that spend arguing with each other, the less chance any of the rest of us will have to encounter them.
And supermarkets:
But I think a supermarket checkout is a gray area (it's all the plastic). The big retail chains have spent decades mechanising and dehumanising the shopping process ... So it's not particularly surprising if customers no longer behave like they're popping into Arkwright's for six ounces of gobstoppers.
Read it all. The Comments are also of interest.