Next to sleeping naked, this is something a lot of people have done at least once. Whether as a practical matter on a hot day in a remote area, or on a dare. I used to go backcountry camping a lot, hiking for days, carrying everything I needed in a backpack. It's hot sweaty work, and going for days without a bath gets old (not to mention, smelly). In many places, there's plenty of opportunities to slip into a lake or stream without anyone else being around. Doing it naked is a matter of practicality... No wet clothing to have to wait around until it's dry. Plus, it's much colder to be in wet clothing, than to be naked. And it's nice to just "air dry" and move on, without carrying anything wet.
On a dare, alone or with others, there's way too much anxiety attached. It's an uncomfortable situation with others around (until you get used to it), and when alone, you're worried that others might see you.
But if you give it a chance, the first thing you notice how nicely you just glide through the water without the drag of wearing a swim suit. And it's really really nice to not have that heavy wet nasty clingy wad of clothing around you when you get out. The water just sheds off you and you dry much quicker and more evenly than if you're wearing something.
We have completely private back yard with a pool and a hot tub. Needless to say, neither my wife or I wear a stitch using them if we can at all help it. It's wonderful to just jump in without having to change into a swim suit or change out of that wet nasty thing each time. All of which makes going for a dip more spontaneous on a hot day or when doing chores. You don't need anything you don't already have, and you dry quickly without any fuss, change back if need be, or just stay naked afterwards, if you can get away with it.
We don't make a big secret of it (we even have a playful sign by the pool to that effect) and anyone is welcome to swim naked in our pool whether we're around, or not.