bang bang, or the double bang, as any unix junkie could tell you, is used to repeat the last command you inputed into the shell. Very useful for repetitive tasks.

As any professional wrestling junkie can tell you, "Bang Bang!" is also the catchphrase of Cactus Jack, one of the personalities of Mick Foley. At the end of every promo, Cactus Jack would hold his hands in the shape of a gun and pantomime shooting into the air twice while shouting "Bang Bang!".

A play in baseball when the runner and the ball reach a base or the plate at almost exactly the same time.