Whenever I've been on a camping trip in the back country, something about taking a leak or dropping a load outdoors gives me a hard-on. One fairly recent trip was to the Southern Sierra in California for a four-day hike with a couple of guys. As usual, when one guy says he has to take a leak, most everyone else is ready, and each guy finds a tree with his back mostly to the others to piss on. Even though I try to keep my mind focused, I can't help it and always get hard during this ritual. (Does this happen to anyone else?) The result is that my pee starts out streaming down to the ground normally, but by the time I'm finished, my pee stream is a dead give-away that my dick is hard and pointing straight up. So far, no one has said anything about it. And it's really tough to find private time to satisfy my hard cock after this.
One way I've managed is to take a hike away from the others, with the pretence that I need to take a dump. Once out of sight, I drop my pants and squat down, my by-now hard dick sticking straight up. Now I can jerk and cum in the fresh outdoors, and oh what a feeling it is.