I think it's always all right, given it's done appropriately, to say it when someone has a behaviour you dislike. That being said, it's also all right not to want to please everyone. And wanting to please everyone can be quite bad.
I say, you do what you want, but people also say what they want. Anyone doing something daring should understand that more sensitive people might criticise. Whenever you stray from what people tend to find okay, you'll tend to have more judgemental looks. From that point on, you decide what you do.
I can't reasonably speak too much more because I'm biased: I also tend to disapprove of an excess of cleavage, as well as I tend to immediately try to change what displeases people.