I was watching an adult video at my friend's house and I couldn't hold back any longer, so I started masturbating when my friend left...but my friend's sister saw me! Then my friend's sister said she wanted to masturbate too, so we showed each other our genitals! We got really excited about showing each other our genitals and masturbating together! We even had sex in my sister's room, hiding from my friend when she came home!