When something is pretty bad, not talking about 9/11 or anything like that, or it disgusts you.
The bang is also an expression to explain deep unhappiness and frustration.
Cannot be confused with the bang bang.
Trying to slang the bang bang down to the bang offends not only those who wrote the urban dictionary but also the entire english speaking population.
A victim in a Saw film, it would come out saying that the experience was the Bang.
A guy gets run over by a bus, His luck can be compared to the Bang.
Charles says to a waiter "Ahhh this food looks the Bang!!"
Phil says to the waiter "Oh don't worry, Charles doesn't like it, could you take it back please?"
In conclusion, Charles thanks to Phil is now a happy man.