The practice of turning a handgun sideways when firing to impress and/or look cool. This is quite common in movies these days (especially those with a little gangsta flavour) and even some games (in Unreal Tournament, for example, you can accomplish this by pressing alternative fire).

I can't for the life of me figure out why. The barrel of a gun is slanted slightly upwards to correct for gravity; this would mean that if I fire gangster style with a gun in my right hand I'd hit low and to the left of my intended target. About the only use I can see for it is if shooting repeatedly in a crowded environment at close quarters and I dont't really care who I hit, the recoil would jerk the gun to the left instead of up, thereby slightly increasing the chance that I hit the guy to the left of the target. But how often does that happen? My theory is that the gangster firing style is adopted just for the sake of coolness. And let's face it: it just looks stupid.