I make a USA distinction here.  Most of these decisions will be poor anywhere in the world.  But, some of them will be more offensive in the USA.

1. Failing to read the posted rules. Every beach has rules. Clothing optional beaches tend to have more rules. Read and follow carefully.

2. Forgetting a towel.  Sand + bare butt = bad.

3. Forgetting to apply sunscreen everywhere.  Especially on parts that don’t usually, er, see the sun, if you know what we mean. (And don’t forget to reapply!)

4. Expecting a scene out of Playboy or Chippendales.  Trust me, nude beaches are only packed with perfect bodies in the movies. It’s liberating seeing so much "imperfection".

5. Using a selfie stick.It’s obnoxious in places where people have their clothes on, so…

6. Close talking.  You don’t like it when people invade your space with clothes on, right? That goes double for a nude beach. Americans prefer three feet of personal space in everyday life, so make it six when naked with strangers.

7. Taking pictures.  This is not the time or place for Instagram, people.

8. Staring.  Need we explain? Don’t be that creepy guy.

9. Running.  Even Baywatch babes needed a swimsuit to look good doing this.

10. Engaging in PDA (public display of affection).  When you’re naked, everything takes on extra meaning. If you can’t keep your hands off your companion, put your clothes on and move back to the regular beach with all the other gropers. Or get a room.

11. Doing yoga poses.  Don’t subject anyone to certain angles of your naked body. The beach yoga photo for your Facebook page will have to wait.

12. Neglecting to have a bathing suit or cover up handy just in case.  Food and recreational facilities nearby may have no affiliation with the beach, and may have health codes to obey. Plus, you need to wear something back to the car.

13. Being ashamed of your body.  Going to a nude beach is supposed to be liberating. It’s not about perfection (see no. 4). If you’re going to spend the whole day squirming, it’s not for you.

14. Making small talk.  Conversing with strangers is such a common habit, it’s easy to forget that in this context, not everyone wants to chat. And if you do find someone who wants to have a conversation, look ‘em in the eyes, buddy.

15. Going with a brand new friend or significant other.  TMI, my friend (unless they are also an acknowledged nudist).

16. Bringing the kids.  This isn’t France.

17.Bending over.  Crouch, don’t bend. You don’t want to give everyone more of a view than they bargained for.

18. Doing anything that could accidentally cause, um, arousal.  This one’s for the guys.

19.Having no shame.  You have to be respectful of the people around you.

20. Failing to hydrate.  Ever see anyone with heat stroke while naked? It’s not pretty.

21. Eating snacks with lots of crumbs.  Again, too many skin crevices, like with the sand.

22. Neglecting to manscape or groom properly.  This one’s a personal choice of course

23. Going with major bikini or tan lines.  Don’t be a cotton-tail - it just looks funny. But everyone must have a 1st time. Be sure to note #3.

24. Using a pickup line.  Unless your ego can withstand the obvious observational comebacks from the now-completely-disgusted object of your (unwanted) attention.

25. Behaving differently than you would at any other beach.  The general rule at a nude beach is to behave normally. So unless your “normal” self is a lewd, gawking, selfie-taking greaseball, strip down and act naturally. It’s what everyone else is there for.

Any other poor decisions to avoid / rules to abide? Add them in the comments.