If you understand how masochism, the pursuit of pleasure through physical pain, appeals to some, then think of humiliation as the pursuit of pleasure through emotional pain.

To be called a slut or whore, exposing ones inner desires for themself to see, or others to see, can be very liberating. Throw off the shackles of a society that says you have to be and act a certain way... put yourself into the emotional hands of another... and perhaps you will begin to understand.

In the physical throes of an orgasm and being told you're a dirty girl... can range from mild embarrassment full through to humiliating. It's not the humiliation that's important, it's how it powers the mental fugue of orgasm that makes it enthralling.