[MayflowerMadam]

“Why?”

In the south, “Bless your heart” = “Up yours.” In a sweet way, y’know. I love the language of the south and am finally getting the hang of it after two years in TN.

[SuziQ]

I say “Bless your/his/her heart” all the time, and don’t mean it in a nasty way. Depends on the context of the conversation.

[lovecraft]

Bless your heart can be used that way, it can also be meant as a term of deep sympathy if the person has had anything from a bad day to a tragedy.

The "up yours way" will generally involve a smile and it's always in reply to something snobby in my experience.

This is SC, so your mileage may vary when crossing state lines... :)