I reckon there are many kinds of platonic friends in this world. One of these kinds is opposite-gender-platonic-friends. You love them. They're your friends like all your other friends. They're either simply fun to be with, or funny, or share common interests with you, or you can deeply talk to them, or whatever. All in all, they're just like all your other friends.

But. (Why is there always a but?)

The thing with these, is that they're always right. Especially the brand known as the female-platonic-friend. More often than not, she'll be right about everything. Very, very, very rarely, she can go wrong (try having her navigate while you're driving, that ought to break her correctness algorithm). More importantly (read: annoyingly, frustratingly), she is always right about everything that matters.

Let me demonstrate:
Friend: This is gonna go all wrong. Stay away from her.
You: Oh, come on [place name of friend here], I don't even want her. So what if she has a boyfriend. We're just friends, like you and I.
Friend: Shuts up, only nods with a knowing smile.

Another variation:
Friend: She doesn't want you.
You: But [countless reasons here, how much fun the two of you have, how she laughs from your jokes, how she touches you all the time].
Friend: Shuts up, only nods with a knowing smile.

And that's it. It's over. Lightning's struck. Whomever it was you were telling your lady friend about, you're through. If you're young and inexperienced with such lady friends, you'll do the absolute rational thing and go against her advice (advice which has absolutely no basis in facts, so help you god). <voice tone=sinister>canned laughter</voice>. Big mistake. It will never work out. Three years from now, after the next->next heartbreak, you will find a note your lady friend wrote to you in class, or browse your ICQ logs, or whatever, and you'll be damned, there it was written, The Future.

It's a good thing that humans, like most domesticated animals, can be trained. After the third or fourth time, you'll start being afraid of telling your lady friend things, lest her judgment be harsh. You can run, but you can't hide. She will read you like a book and ask "what's her name", even before you finished saying "Hi!" and flatter her new [dress|earrings|shirt|shoes|.*]. So you'll tell her all about it, and as soon as you finish your tale of the intelligent, beautiful, funny, geekgrrl you met at the party last night, who can dance like you never danced in your life, you will look at your lady friend with a hopeful gaze and pray that she won't be negative. Because you know, you know. All it takes is a knowing smile and a nod, and you're done for, buddy. Do not pass go, don't collect $200. Lady friends are right whether it be good news or bad news, but kill me if I know why, they're more right when it's bad news...

That's basically it. You learn to live with it, having a future-gazing-oracle available within a few keystrokes or a cellular call. Sometimes, it can be quite painful to see, in retrospect, how correct your lady friend(s) are. Too bad, better luck next time.