An intended derivative and omission of “nice” from the
far more colloquial “have a nice day”.
Said as a bare minimum “polite” response when one is aggravated or
feels sleighted.
It’s polite in the sense that it intuitively sounds like have a nice day and basically implies that the speaker cares enough about the recipient that they hope the recipient doesn’t
die...at least for
today.
However it’s also borderline rude, and could be perceived as a
way of indirectly telling someone to fuck off, depending on the context. It intentionally omits “nice,” implying that the speaker is either in a general not-nice mood, or does not care about the recipient enough to wish them a nice day per
se. Still more graceful than telling someone to piss off, as you can always feign ignorance to any malicious intent.