Other mistake: When Memphis and Kip are hiding from Johnny B and his crew in the cafe following the ambush, Memphis devises a plan to make good an escape. He sends Kip out to use the tow cable on the heavy tow rig to destroy Johnny B's Mercedes. First angle shows a cable wrapped around a rear A-arm of the vehicle and the hook connected to the cable, the next shows a hook directly attached to the front axle, which is the one that gets torn from the Mercedes when the tow rig pulls away. Additionally, a different cabling rig and loose cabling used in the stunt are strewn behind the car. So even if Kip somehow made 2 connections without being seen or heard, the rear rig is different than the one shown in the first shot. (00:51:00 - 00:53:00)
Other mistake: Donny steals a older Jaguar from a parking garage in one scene in the movie. Yet if you look at the blackboard with the list of cars, you'll see that there is no older Jaguar like the one Donny stole. There is just the Jaguar XJ220 (that is dropped off near the end of the movie) and a '99 Jaguar XK8, both of which are the newer models.
Answer: He sits on his hand until it goes numb, and then masturbates. "Stranger" refers to the fact that it feels like someone else is doing the work for you.
Nick N.