I did this a few weekends ago. Hope you like it. I only get off on true/or first time stories.
One of my favorite things to do is outdoor sex, which usually is jacking off. It was a really nice day and I was riding my mountain bike in a local recreation area. I was just out for a ride, but was horny as usual and it just happened that the trail petered out into nothingness, basically undisturbed forest. I wanted to get cum, couldn't get it off my mind. So I found a nice spot surrounded by some rocks.
I had on my skin tight biking pants (no stupid pad in the ass), a T-shirt, and some soaked sneakers. First I just pulled off my shirt to lay on in the leaves and began to rub myself. My cock and balls are shaved, a brand new thing I dreamed up only days before. The talc I put down there was still slippery and my nuts felt great. I had my legs spread as best as the spandex would allow, but I wanted more so I pulled them off so I could really spread out. I was really hard and leaking. With precum and spit I had a great slipperiness going on and was rubbing by balls and chest, and stroking myself, touching my hole too.
The last thing to go were the sneaks, which were a distraction, and then I was totally naked, my favorite. I masturbated harder and knew that I would blow my wad shortly. Then I had one of those great cums, ya know, the ones that come on slow and just get massive till the jis flies out. Most of it went on the ground.
I enjoyed the breeze and sun for bit then packed it in to finish the ride.