A girl who is really only interested in a guy because he has a nice car, and it gets him attention, so she wants in on that attention and uses her ass as a free ticket to the car.
If played right by the guy with the ride, he gets to rail a girl outside of his reach because he does have a nice car (or truck... something shiney, tasteful and/or loud)
"Use me for the ride, I'll use you for the hide"
"Man, you seen Ditmeyer lately?"
"who, that geeky guy?"
"yeah, he's nailing Cindy Hotbody!"
"ooh yeah! she's on him because he's got that sweet dub!"
"damn, she's a tirebiter"