While both of our parents were away on a trip, my younger childhood friend came to stay at my house and we were left alone. My childhood friend, who I've always thought of as a little sister, innocently said, "I want to take a bath with you like we used to!" and took me to the bath and started to take off my clothes defenselessly! I didn't know where to look, and she was touching me in all sorts of places, so I got a full erection! I managed to hide my erection at the time, but I couldn't stand it anymore when my childhood friend wandered around in a bath towel after a bath!