Simply put how do you go about creating appeal for an asshole of a character?

The MC in my story is a psychotic bitch who only gets worse as the story progresses. She's vain, bitchy, addicted to drugs, sex and plastic surgery who has become an extremely cold, emotionless shell. She does have a rather disturbing sense of humor though.

She's the bad guy of the story, and I want people to want her succeed in her devious goals. It's proving to be pretty hard when she's rather stereotypical.

Here's a few examples of characters that come to mind.
* Patrick Bateman from American Psycho
* Light from Death Note
* Hannibal Lecter
* Anton Chigurh from No Country for Old Men
* Dexter

You get the picture.