It is the position that the driver of said automobile assumes because of the adjustment of the seat. In attempt to be cool or hip, the seat back is cranked back to the point where the driver feels he/she has attained cool status. The "hunch" aspect of the description becomes apparent when the vehicle starts to move, because the driver, who can't actually see out at this point has to "hunch" forward to see who might be looking at him/her, or maybe even to drive. This is often compounded by the fact that the driver is, for whatever reason, wearing his/her hood up (inside the car!), and can barely operate the vehicle. Should we call it the moron hunch?
The seventeen year old suburban male is often afflicted with hoopty hunch. If the windows are not tinted, he can be spotted with earrings, and wearing his hat backwards, driving his grandmother's 1991 Coupe De Ville. He longs for the day this baby becomes his and he can put 20" wheels on it. But, for now, the seat adjustment is the only grandmother approved modification.