That's interesting, I once watched a TED talk about this kind of thing and it was a tiny bit similar. It was basically saying that, everyone needs to be multi dimensional, for example, some one can be really funny but if that's all they are it would get boring really quickly, similarly someone can be gorgeous but again it would get boring if that's all they were. "Bad boys" if you will are multi dimensional apparently in so much that, they will be funny and clever, or charming and kind etc etc... but have an edge to them thats just a bit different. Apparently it's a subconscious thing you get attracted to. So like what she was saying, they're kind to "you" but could be harsh...
Was an interesting video and probably made way more sense than how I've wrote it! I'll see if I can find it and post it up!