In Northern Ireland on operations we were constantly under threat of being car jacked by the opposition (the terrorists), as we drove around in civilian clothes carrying 9mm pistols.
We were trained to do this:
1. Someone appears and wants your car, usually associated with having a pistol or AK47 pointed at you!
2. Behave like an ordinary person and give them the car - they have no idea you are armed and know what you are doing.
3. As soon as the opponent is in the driving seat, immediately move to the front headlight area of the car (but not directly infront of it!!!) and draw your pistol
4. Issue a challenge - 'Stop or I Fire'
5. If they even twitch - give them a double tap to the face
6. If their passenger twitches - repeat step 5
It's simple and effective; the majority of the time the people who are hijacking you are amateurs who have been told 'here's a gun, go and get me a getaway car for a job I'm doing'. The main players are at their holding area awaiting the car so they can do their task.
9 times out of 10 when you do this to the 'car jackers' they require clean underwear and a reserved cell at the Police Station.
PS. It also requires balls of steel to do well! (which is British-speak for having big Cojones!)