Use a vehicle to ram a motorcycle with two people sitting on it. Make sure you hit them hard enough so that they both fly off the bike. Then, get on the bike and shoot the driver, but not the back passenger. If done correctly, the remaining passenger will hop back on the bike and sit behind you as you drive around. Note: You will not be able to bail from the bike while moving, as the back passenger will block you from being able to jump off. To get rid of the passenger, just get off the bike and shoot him or her.