A couple of years ago now me and my sister were out shopping and we always used to play tricks on each other so we were walking through this shop and slowly from behind I lifted her skirt up so everyone could see her knickers. This as you can imagine annoyed her but she didn't do anything, which I thought was strange. Later on we separated when I looked at cars and she at perfume. The all of a sudden she came up behind me and whispered in my ear "REVENGE" and before I had any chance to move she yanked my shorts down, and with added bonus for her my boxers as well so I was naked in a shop infront of everyone my balls and penis in public view. I was 12 at the time and she was 14.