Heard it all my childhood in the 60s. Early childhood in Northeast Kingdom Vermont. Later childhood in the County. Sounded more like ah fa than ah va to me. Don't know if it was specifically Franco, but obviously most childhood companions were Franco in both places, so . . . related to faux pas, maybe? Said with shocked expression and sharp intake of breath.

Only kids said it, never adults. Clearest memory, someone's little brother clowning around put a rosary around his neck like a necklace. He got ah fa'ed from all sides and his older brother told him Jesus was gonna come and sit on his neck. He took it off immediately.