Some people will give you a swat on the butt for the sake of being light-hearted and playful. I was sometimes spanked in a playful manner by my parents, even when I was a young adult, but at the same time, I wasn't wearing diapers at the time. I wasn't particularly bothered by it, but that swat on the bottom often came at an unexpected time. If someone is making you uncomfortable with such light-hearted spanking, let them know it makes you uncomfortable and tell them to stop.