So this happened less than a week ago. Sounds like a clickbait-y buzzword kind of /r/gonewildstories title, but this is 100% true.
My and my stepsister’s parents have been together for a few years but don’t live together, so I rarely see her. We’re both 18, both still in high school, and both get along really well, but I’ve never really felt any sexual tension, despite the fact that she’s 10/10 model gorgeous. She kind of has this hippie/hipster blonde chick thing going on that I usually wouldn’t go for, but works really well for her.
Anyway, we were recently on vacation and watched a movie in her room with both our siblings. She was wearing a big loose shirt and loose cottony shorts. I fell asleep about halfway through the movie and woke up to find her sister asleep next to me and her still awake, scrolling through her social media. Everyone else had returned to their rooms.