Alyx Vance. I'd get her good and drunk and take advantage of her. Not because I think she's cute, because I just hate her that much. Well, and because she's cute, and I'm not enough of a jackass to take her into a dark alley and beat her. Oh, and after playing an emotionally oblivious, mentally lacking, mute that she wants to go down on I've found out that she's rather easy. I never thought I could hate a fictional character so much until her...
...I might as well do a nice answer to counter that... Lucy, from Assassin's Creed. I'm sorry, I'm Native, so if I could convince her to let me use the Animus I could relearn some erased history and be completely bad-ass while at it.