There are plenty "alternative reality" stories, with different social rules. Most typically go for extreme, like "women never wear clothes", which to me are mostly ridiculous, for many reasons, like practicality of shoes, hats and pockets (and weather, I live in very cold climate).
So, my idea is, an alternative reality, but everyone is required to spend only one day a month in the nude, and it is not complete nude, shoes, accessories, bags (ID bages, lol), and similar clothes items are still allowed. More so, for those, not willing to go full nude, there's an option to spend three days (in 1-2 ratio) either topless or bottomless, and people, who need to wear protective items have them in see-through variant. I also believe, such alt reality would be a lot more fun, if played like "aliens conquered us and make us do that", so it is something new, not something normalised through culture. (don't forget that those pants-less people need towels to sit on. I can believe in strange worlds, but I can't believe in worlds of 100% clean butts)
Thank you.