I would not be rude if I said to a smart person "Hey, you've got a brilliant mind." Why is it wrong to say (or think, or imply by ogling) "Hey, you've got a beautiful body?"
I know that this is not the scenario you're talking about but bear with me here, cause this one goes all the way around: I think either of these statements, if said to a total stranger, is creepy in its over familiarity, and that it takes time and a foundation of understanding before one's opinions of another aren't based on untested assumptions. It's about healthy boundaries. At a certain point in knowing someone, platonically or otherwise, it becomes okay to have emotional intimacy, and conveniently enough, this time often comes ones you've figured out the persons nature and sensabilities, where as, if I see a hot lady in the locker room who I've never met before and say " I really admire your breasts" that is not appropriate or healthy behavior. When you look at kids with FASD for example, these kids have a total lack of boundaries, which often makes them incredibly loveable - they'll slather you with compliments, and both ask and assert intimate things about a person they've just met. This seems all well and good, but then kids with this disorder have a staggeringly higher rate of being sexually exploited. Due to the same lack of boundaries.
So we have the one scenario, which is a "you don't know me, you don't have the right to cross that line" thing.
Then there's the other one.
What I'm coming around to is this: once you know someone well enough to say you actually care about them (platonically or otherwise) you
should be able to compliment them on any aspect of who they are, but damn if this isn't always possible. You can know a lady, know her really well, have a caring friendship (or more) with her, and say something genuine about why you appreciate her. The thing you say may be complimentary to her physical appearance, or sometimes even her mind, and that woman might be glad for it or instead be hurt by it, get upset and not be okay with that. Why? Lots of ladies have dealt with a lifetime, or even generational damage. She may have had a mom, a boyfriend, a brother, a teacher, whoever, who shoved a hot poker right into the core of her self esteem. Which is often, when it comes to ladies, rooted in an attack on her physical appearance. Many ladies walk around with a perminant sore spot that may be even too painful or too deep to even acknowledge, that has cause them to be off kilter with boundaries in the other direction. Where some ladies struggle against letting kindness in, and where kind words can even hurt like a slap in the face. That Bruce Springsteen song "Secret Garden" touches on it really well. There are certain places within some women, that they may never be able to allow a man to access, even if he is indeed kind, loving and everything wonderful. You can be (and I know many of you guys are) genuine and true and lovely, but in a situation as immediately as her last or current relationship with someone else, a women can totally hate a part of herself so much that she'll hate you for loving it. Or in a situation as far away as her great grandmother's generation, something horrible might have happened to women in her family, done to a woman by a man in a time where a woman was a piece of property, and beating the shit out of her, raping her, whatever, was allowable. Then that great grandmother bread a distrust of all men into her daughter, who passed it on to her daughter, who passed it on to the beautiful woman in front of you.
It is the wreckage of gender. Like race, it's the rigid divides and all the crap that came with it that makes it hard for people on both sides to now know how to start again. In North America, I believe we live in a time of hope, because we're a ruling generation beyond starting to see those divides as false now. This isn't to say crimes based on gender and race aren't happening as I write this, but really, really, I think we're coming to a point within history where we're actually acknowledge arbitrary divides as arbitrary and that's exciting to me.