A childhood belief about swearing

When I was 8 or 9 I was walking through the ravine with my friend who was a year older than me. Some boys were giving us a hard time, so she yelled to them, "Stop it you sonofabitch!" and clapped her hand over her mouth. I asked her what that meant, and she said, "It means son of the devil...I think." So when I got home, my Dad was entertaining an old friend of his from the Navy and I walked in and said, "Dad, what's a sonofabitch?" and he nearly flew across the table to strangle me, but his friend pulled him back, laughing, and told him to relax. He didn't tell me, but I knew it had nothing to do with a devil!