How do I make things up to my boyfriend?

My boyfriend has been giving me the silent treatment since last night. I'm currently pregnant with our first baby and we were just discussing parenting. He has a son who's 11 and is here ever other week. We had a conversation on our opinions of spanking and he said he's never spanked his son ever. Then told me a story about in high school his parents signed that paper that allowed him to be spanked and that he doesn't know if this was legal but his principal would take him into a private room and make him get completely naked and spank him with the paddle. I laughed. Idk why. Just the image to me seemed funny. I didn't realize it truly traumatized him. He said it's not funny and now I'm not only laughing because I thought the image was funny but how I'm also nervous laughing. He got mad and went to sleep on the couch and doesn't want to talk to me. I feel bad and I wasn't doing it to upset him. With the sound of his voice when telling the story I didn't think he was super traumatized. I think I also didn't register he was saying he was naked when spanked and how that could be traumatic.