In south Georgia, waiters and cashiers at stores often say "have a blessed day" to me. It happened to me three times yesterday! I need a snappy comeback. I've tried "thank you, Jesus" and "thank you, father". I've tried "well, bless your heart" because that is sort of derogatory if you are speaking about a third person, but probably not if you are speaking to another person. I need suggestions!
I don't bother replying in a negative way; I realize that for believers that's their way of saying "have a good day"
Depending on context there are times I'll bring up my non-belief but thank them anyway, but most times I just say l tell them to have a good day as well