My friend Amanda describes it best, as far as I'm concerned. I call it the Peach Metaphor.
It's like you're walking through the Garden of Life. And you find a big, ripe, juicy peach. And you pick up the peach and it seems to whisper to you, "Go on. Take a bite. I'm a succulent Dating Peach. Bite me and we'll be happy together."
And so you start to bite into the peach. And then suddenly the peach starts screeching, "Hey! I'm only a I'm-Glad-We're-Friends Peach!" And the juice tastes sour and you have to drop it and go off to look for an actual Dating Peach. But the bitter savour of that last misadventure has put you off peaches entirely. In fact, you don't even want to walk in the Garden any more, you just want to sit in bed eating from a big jar of Mallo-fluff.
I have but expanded upon Amanda's original thought that boys are like peaches and there is always another one out there to take a used-up, bitter peach's place.
Besides, at this point I'd damn well rather have a cigarette than a peach anyway.