Once I was with a female friend at the beach, and we were alone there. It was a sunny hot summer day and she lay on her back next to me. She wore a bikini and I wore a pair of shorts. As I lay next to her I couldn't help watching her body and the sight of her perky little titties and her slim body made me aroused. We had just had a swim and her wet bikini made her nipples quite obvious. As she had her eyes closed I even put my one hand down my shorts and stroked my cock discretely. It felt so nice. After a while she turned around and lay on her stomach. I quickly removed my hand so she wouldn't notice what I did. Then we talked for a while and then she turned her face away from me, so I continued to masturbate, still discretely, while fantasizing about her. Soon I felt my climax was getting closer, so I had an idea. I asked her if she wanted me to put some sun lotion on her back and she said, still facing away from me: "yeah i think that's a good idea or I will fry like bacon". "Ok just give me a minute", I replied. I got up and stood on my knees right next to her and pulled down my shorts and started masturbating like crazy...my cock was rock hard and the whole situation was such a turn on that I started climaxing immediately. I shot my cum all over her naked skin.. a couple of really messy streaks over her upper back, her shoulders and neck, and then a final cumshot over her lower back. "Woa! woa!" she said, "go easy on the lotion". But she didn't turn around. So I just pulled up my shorts and started to rub my cum into her skin, very slowly. It was amazing. But the cum dried out quite quickly. After about 30 minutes we went for another swim, and then we left the beach. She never figured out what had happened.