As an older sister, I personally taught my younger sister's boyfriend how to have sex! My cute younger sister (a high school girl) brought her boyfriend home for the first time. I was relieved to see that he seemed like a serious guy, but... he's in his teens, so if they were alone in their room, they were bound to do something naughty... Worried, I peeked into my sister's room... and sure enough, something naughty happened...