Green's notes that gnarly can be a term of disapproval, meaning “bizarre, frightening, amazing,” or, conversely, it can be used to describe something that is “wonderful, first-rate.” It was popularized by Fast Times at Ridgemont High (1982).

When did the word gnarly become popular?

Gnarly has been around since at least the 1800s, a form of “gnarled,” meaning knotty—gnarled hands, gnarled tree branches, et cetera. Surfers started using it in the 1960s, describing dangerous waves.

Is gnarly still used?

The word "gnarly" is one of the most commonly used expressions in surf slang. Wave riders have been using it for decades. ... The expression often comes out of a surfer's mouth when something simultaneously spectacular and unexpected occurs. However, you might also have witnessed it being used in a derogatory way.