For the cooler mathematicians of this world, "bang" is also how you pronounce the factorial function, "!". As in,
4! = 4 x 3 x 2 x 1 = 24
6! = 6 x 5 x 4 x 3 x 2 x 1 = 720
etc, where 4! is pronounced "four bang" and 6! is "six bang".
I swear, I'm not the only one who does this. (There are even some people who say "four shriek" instead.) Of course, there are stick-in-the-muds (sticks-in-the-mud?) who insist on calling this function by its proper name "factorial". But seriously, folks. "Four factorial" is dull and boring. "FOUR BANG!" is FUN to say! No wonder people think maths is boring! We're giving this science a bad image! Just think how much more fun it would be if "+" was pronounced "squelch!"