I once read the book Class: A Guide Through the American Status System by Paul Fussell. There, he mentioned that saying “Have a nice day” was a faux pas, without elaborating why.
I’m not American, this is way too subtle for me and Google did not help. Therefore, I’ll ask here: what is wrong with this phrase, and what should I say instead in situations where I would use it (like for example parting with a person)?
I’m not making this up, either: look at the first paragraph.