Urinating off a cliff. Catching air with your private waterfall while setting it free from a great height.
It's yet one more guy thing.
If done often enough, it will result in a pecking tan, which is usually only a byproduct. Deliberately trying to get a tan where none should appear is not approved behavior. Keep that in mind.
But if done at all, this procedure is most wisely practiced in isolated spots (preferably sunny of course if it's a tan you're after) where no roaming posse of Sunday school teachers is likely to tread.
Probably a hobby best pursued alone. And check for who might be walking by, down there, while you do it. Or you could get pounded.
This is never, ever, ever done with other guys unless you really, really, really mean it, and are under 10 years old, and immature for your age.
Sort of stupid though because you'll probably get your feet wet in the process or end up with a weird tan line along the zipper. If it's a tan you want why not go to a nude beach and get an all-over? Eh? Or buy a sun lamp.
Or something. Geez. What does this have to do with hiking?
Too much sun exposure may cause distinctive permanent skin spots known as "peckles". And how do you explain them?