What is the origin of the idiom "double whammy" and when to use it?

The idiom "double whammy" is believed to have originated in the United States in the early 20th century and is used to describe a situation where two negative events happen at the same time, compounding the negative impact. The term "whammy" is slang for a curse or jinx, and the "double whammy" is a situation where two curses or negative events occur simultaneously, making the situation even worse.