Vaguely rude?

Has anyone the answer to meaning of the phrase: "How nice for you!"
I take it as vaguely rude?

It's sarcastic. Meaning, "Who cares. Not me."

It's inconsiderate, but not so rude as I'd take offence. Shrug it off.

It isn't necessarily rude at all. It can be an expression of pleasure at another's good fortune or success.