Let's say you decided to show curiosity in the last question. Newton's third law states that the force acting on the bullet will equally reaction force at the gun, and since the weapon is in your hands, then you. Due to the fact that in the open space you will not find such a density of atoms as we do, you need to cook you will begin to move in the opposite direction. And if the bullet leaves the barrel at a speed of 1,000 meters per second, then you will move much more slowly (a few centimeters per minute), but only because you are more massive than it.
After firing the bullet will go on forever. "It will never stop, because the universe is expanding faster than the bullet reaches any serious amount of weight" to slow it, said astronomer Matija Cook. The same awaits you.
If you decide to shoot Jupiter (which happened to be quite close), you can even not specifically aim. Bullet simply "attract" the planet, and with such force that its speed will increase to 60 kilometers per second.
Shoot someone in the back - this despicable act. But in space, you are "theoretically can shoot yourself in the back", - says astronomer Peter Schultz of Brown University. He believes that this can be done while in orbit of a planet or, for example standing on top of the lunar mountains. In this case, the bullet will return to the point from which was released (ie, you). But keep in mind that you also have to set in motion, and the surface of the Moon can not be "smooth".