Actually, I make that a staple shot whenever I'm taking stills. It's a personal preference (the "fuck you" pose) because I like the attitude that the model can project with this shot.
I've been collecting them for a few years and have them together in a portfolio titled "Pornstar Attitude".
A variety of simi-nude to hardcore shots, each with the starlet making a rude hand gesture towards the camera. Not just the middle finger (American
style) but whatever native finger flip they grew up with.
There's something about aggressive girls gets me going.