What is happening in this picture?
The model is exposing himself to us.
He sits on the corner of a car's trunk, legs slightly spread. His crotch is dead center of the image. A tarp, pulled up and tucked beneath his crotch reveals the car beneath, reinforcing and doubling the expression of "exposure". The position of the gathered tarp and exposed, protruding portion the the car draws further attention to his genital region and focuses energy into the image's center.
This is not a flirtatious exposure, but a menacing one, as is clear by the model's non-verbal expression. The fact that he is sitting on a car also has communicative significance. If the car belongs to someone else, it is an act of dominance and transgression. If it belongs to him it is a display of possession, of "owning".
It is no accident that the tarp is blue (jeans are blue) and the car red (the color of genitals flushed with blood).
Is it going too far to look for further connections between the car and sexualized behavior? Cars, in the context of advertising, are often fetishized sexual objects. Acts of indecent exposure often take place in modes of public and private transportation.