The way a Linden once explained it to me was that it was NEVER acceptable to be naked in G areas. The reason being "A dressing room" is only an illusion of privacy. The reality is anyone can cam into anywhere. There is NO real privacyc in SL.
We may not like it. We may not think it makes sense. It is just how it is.
Now the reality of the grid is, you have to get reported for anything to be done about it. But yeah, someone could report you for being nakie in a G sim if they wanted to.