Why are the cute ones always crazy?

There is this girl in my graduate class, who recently graduated college, etc (meaning she's young). She's kind of cute and has a fat behind, and was someone whom, at first glance I wanted to have sex with.

However, she's crazy. But not Zoey Dechanel, quirky, flowers-in-her-hair doesn't shave crazy. No, she's kind of bi-polar. She has this front as being super-enthusiastic about everything she's into, very gregarious.

She's the type of girl who comes across as being flirtatious and sultry, but she'll deny this of course, right. Shame on you if you thought you had a chance with her. She's new-agey and "empowered" at least in her head.

But really though she's full of sh!t. She doesn't have a job, stays out 'til 4am several days out of the week, wakes up at noon, etc. But in her head, though, she's all about getting sh!t done--she's the dragon warrior. Yet she has no real life experience and knows nothing about what it actually means to work-hard and sacrifice and be resilient in the face of adversity. Moreover, the kind of men she is into are ghetto thuggish types, despite her front as some kind of student of world events and social activist and what-not.

The kind of guys she goes for have a rap-sheet, are on parole, have 2 or 3 kids, and pay child support. But in that respect, I don't judge her, I honestly believe that's who she deserves.

But, she's kind of cute, but really not remotely the hottest girl I've seen. I've dumped hotter girls than her. Yet, as a man, I'd wanted to have sex with her, of course.

In any case, at the end of a night of being out with some mutual friends, I tried to give her a kiss on the lips, of course she turns her head and says no. But the way she said no, it was as if some homeless guy was asking her for money or something.

Since then she's totally been ignoring me. The thing is I had subsequently spoken to her on the phone, and the conversation was pretty amicable, I didn't hear any anger in her voice or anything, so I thought we were on speaking terms, at least, whatever. Then, the next time I see her in person and tried talking to her. she was like: "what do you want", extremely impatient, sarcastic, rude. I tried calling her later that night and she hung-up on me. I texted her asking if I owed her money, or something to be so rude, and that I was'nt going to talk to her again.

Listen, I've been around the block a few times. I've known girls exactly like her--brash, crazy, bi-polar, high-on-life, into drama, with a love for dangerous men, but cute--and I know enough to know that they are not worth it. She is not worthy of me, and she has nothing that I want from a woman (except to have sex with her, of course), but seriously, she's selfish, egotistical, the world revolves around her, she has no life experience, no job, she's kind of chubby, etc. All she could ever offer me is heart-ache, drama, disappointment and resentment--things I do not need in my life.

tl;dr Why can't I stop thinking about some crazy-as s girl (who's not even hot) who wouldn't give me the time of day?