When my parents remarried and we moved to a house with a large balcony, my sister-in-law brought her friends over and started suntanning! Then, when I was bored, she grabbed me and asked me to "apply oil" to her, and as I was doing so, I couldn't help but get an erection from her shiny ass and cleavage... I couldn't hide it because I was staring at her, and I thought she would find out and get angry, but my sisters-in-law, who were amused by my erection, gradually got excited and started asking for my dick!