That is what a Southerner says when a car driven by elderly people cuts you off or otherwise annoys you. You just smile and say, "Bless their little heart" and keep on driving.
I have used the powerful expression in groups of women when someone we hate shows up and someone says "look at that dress, could it be any tighter",,then we all say in unison, "Bless her heart", then we all laugha nd laugh and get another margarita.
Whiskey & blood on the highway,
But I didn't hear nobody pray.