Just tell them “bless your heart” Yanks have no idea you are being condecending and insulting to them.. they think you are being kind and sweet.
“Oh, you really believe that? Well bless your heart.”
Its such a great line, its one of the few ways you can insult a person to their face and get a “thank you” from them in return.
YOu’re right ... have to remember to do that more frequently!