As a Texan and a Southerner, I have the double whammy of accents. I write and sound reasonably intelligent, use correct grammar, spelling and punctuation. I open my mouth and all bets are off. Slow drawl, incorrect grammar, drop the "g" in words ending with ing. My speech is peppered with colloquialisms pertinent to the area, plus a lot of crap I make up on the spot.
Nyboy, your friend is on his way to being converted. His life will never be the same. You see, as a group, Southerners are friendly, caring and we overlook idiots from up north. LOL Bless his lil' ol' peapickin' heart.
If he is saying bless your heart, it is obvious that phrase has been uttered to him. Bless your heart can be used as an euphemism to politely replace more inflammatory words such as "You are dumber than a box of rocks." Or, "look up the dictionary defination of stupid and you'll find your name." Bless your heart is delivered with a smile that the unknowing doesn't understand the meaning of. Hahaha.... sure miss those smileys ....
Bless your heart can also spring from genuine caring for one's well being. Bless your heart can mean just that. Bless your heart can mean deepest sympathy.
Nyboy if your friend is being rude or obnoxious, followed by a smirking Bless your heart..... even a Southerner can run dry on patience and politeness. Somebody's gonna smack him up side th' head with a stupid stick.
Now is all that clear as mud? LOL