When i was 17 my older sister walked into my room without knocking to find me pretzeled up with knees by my ears self sucking my own c***. I was freaked out and embarassed. She was just stunned. Then as i stood there with my hands hiding my c*** she asked if she could watch me do it. I did so and it was so hot to do with her watching. It became a regular thing with no other interaction or contact. Fifteen years later i still do it for her whenever she wants to watch.