A blessing overdone?
The OED entry notes that bless can be used in an ironic fashion in its senses of conferring happiness, good fortune, divine favor, and so forth:
- In many senses (esp. 5b, 7, 8, 9, 10) bless is used euphemistically or ironically for a word of opposite meaning, ‘curse, damn,’ etc.
1814 J. Austen Mansfield Park I. xviii. 353 Could Sir Thomas look in upon us just now, he would bless himself.
1838 Dickens Oliver Twist I. xiii. 204 An emphatic and earnest desire to be ‘blessed’ if she would.
1878 H. Smart Play or Pay (ed. 3) viii. 156 Fuming, blessing himself, dashing himself.
In this sense, it is similar to the use of bless your heart (cf.), which on its face is a show of endearment (CDO) but is also used, in Southern (U.S.) English, to cast aspersion cloaked in false affection or sympathy.
One has to wonder if it denotes how inflection is often as important as the words themselves, and so "have a nice day" can mean anything from exactly what it says to the polar opposite of "I can't stand the sight of you any more, so I'm leaving". Or the sort of overly-polite way a commoner might address a lord, sarcastically showing their derision for the title.
Or, for the best literary example off the top of my head, in the manner that Antony repeatedly refers to Brutus as an "Honorable Man" in Julius Ceasar, implying that he is anything but.
Inflection