I once had an English friend who, try as he might, could not pronounce the word «gnarly.» I couldn’t tell you if this is a problem for all Brits or just the one, but boy was it funny to watch him struggle to get his tongue around that word. Gnarly, I guess, is a particularly American word. It conjures up images of surfer dudes talking about the waves they just crushed, or skater dudes talking about the half-pipe they just crushed. I guess, in general, it is spoken by dudes who crush stuff. I think it’s a wonderful word, though. It’s way more specific than «cool.» It makes it seem a little rougher around the edges, not quite as laidback. It also implies something aggressive, like a «gnarly bruise» or something off the beaten path, like a «gnarly outfit.» 

Rad is another one of those skater/surfer dude words that I think we all should be using more. Short for radical, it ups the ante again with the word «cool.»