I've brought this up whenever I've been rigging light stands. And every assistant and model I've brought it up with has agreed that it's the most important rule.... even more important than Rule 2, which is the first that comes to mind because you can get caught with this even if you are a professional photographer with honorable intentions.
See, if you aren't careful with your light stands, flashes, wiring, etc. you could easily hurt your model. I think of this whenever I've seen a lightstand go wobbly. You could be wandering around in the dark and your model could fall. Especially when you are talking about a full-time model, she may not have much in terms of insurance coverage, so if she ends up getting sick or injured, that's going to add up to a lot of money on her part.
And, by extension, if you drop a light on her and give her a good bruise, she may have to cancel the shoot she's got the next day and it'll be all your fault.
This is hard for photographers. Either they really ARE creepy (and generally can't hide it), or they aren't creepy. It's hard being a non-creepy photographer, because you want to say "Hey, models! You can shoot with me! I'm not creepy!" But you know that if you say that, they'll assume that you are really creepy and trying not to be creepy.
If I didn't have to bring gender into this, I wouldn't, but generally female photographers are considered to be, by default, non-creepy. I'm sure if you researched this, you'd find cases where female photographer did the most horrible of crimes to a model, but it's just the way things are.
A shoot goes very smoothly when a model is comfortable around you, you can make small talk with each other, you keep your hands off the model without permission, and are otherwise a polite and affable person.
One time, a model was struggling with her wardrobe change and I looked at her and said "Is there any way I can help you without being creepy?"
I once took a closely cropped abstract shot of a scantily clad model. I figured that she might get concerned about being zoomed in upon, so later on, I showed her the shot and asked her if she was OK with the image. She said that the only thing that would annoy her was if I were to make her look unattractive.
I don't know why, but most male photographers I know have started out with a mistaken impression that getting a model naked is kind of like getting your girlfriend naked. If you want to coax your pretty girlfriend out of her clothes, there's cajoling involved where you have to prove to her that you really DO love her enough to see her boobies.
I've had excellent results being straightforward. I explain things beforehand so there's no surprises. And people are usually pretty good about communicating back that they either are or are not comfortable posing that way.
If you try to gently "talk her out of her clothes" you just end up looking creepy and breaking rule 2.
A model may be showing less bare skin while changing than she did earlier or later in the shoot. It's still rude and makes the model uncomfortable if you watch. Same thing with staring too much.