Is it illegal to be naked in a locker room?

Ha. No, it's a locker room. Don't look at him.

It's not illegal to be rude, which is what he is if most of the other people there are uncomfortable with him being so "excessively naked". That said, the others discomfort with his nudity in that situation is unnatural and inappropriate. Social tensions when someone pushes the envelope a bit are part of life. Sometimes it's for the best, sometimes not. It's how we socially evolve (or step backward).

I do not think this is illegal, lockers rooms are meant to be naked in.

Illegal, I doubt it. If you are offended perhaps you could mention it to him in a polite manner that you are uncomfortable with his nudity and ask him to at least put on a towel.

I've been guilty of the same thing at times especially at the spa where the sauna, steam room, and whirpool are all in the women's locker area.

Ask yourself this:

If you were to walk into that locker room, would you be surprised to see somebody naked?

"No" is obviously the answer....but that question will help you if, unfortunately, you run in to more situations like this one.

"Excessively naked?" I'm not sure how naked a person would need to be to be "excessively" naked but from what you have said, I surely see no reason to believe that this man's nakedness is excessive.

No. Years ago in school we all had to take swim classes, and the boys swam naked.

No,there is nothing illegal about it,but there must be shame which the man does not have.

That's like saying, "Is it illegal to learn in school?"

No it is not illegal