I was 16 years old and I was at the pool with my brother who was 18 and we sometimes play tricks like throw sand at each other but nothing to serious. One day at the beach my brother pulled down the back of my bikini bottom and saw my butt so i wanted to get him back. While he was standing in the water waist deep I went under grabbed his bathing suit from behind and pulled it down to his ankles. He turns around and I see a tiny little wiener with very little pubic hair and I think my brother has a tiny dick for an 18 year old. Then I surface and realized I pulled down the bathing suit of some kid who looks about 12 and I felt so bad for him!! I apologized and left as quickly as I could!