When a man uses his hand to move his penis in the H-Pattern of a manual or "Stick" shifter like he is shifting gears on a car. Often, the man will also use his girlfriend's boobs or vagaina as a steering wheel or clutch pedal.
Person 1: Man, I did the dick shift really hard last night, and her boobs were the perfect steering wheel shape
Person 2: Did you hit the perfect downshift?
Person 1: Yup, and I finished soon after. It was awesome! Will do again, 10/10!