its when you doing something thats super sketchy, or clutch and you pull through by the skin on your teeth. It pertains to anything extreme and psuedo-extreme like snowboarding, skateboarding, a clutch play at madden, a winning shot in a pig game (as long as it was super sick with it), driving like a dare devil. Comes from the idea of starsky and hutch.
I was mobbin down the slopes dawg and i hit the booter, man i was flyin like a squirrel and i still pulled my board under and stuck that sheez... boy you better believe it was gnarski and clutch, i'd been f*** up
Something thats is grows nasty or sick but there is interest and amazement in it. Then ending up being a hybrid of the word gnar and nasty which ends up gnarsty
Joe "Man have you seen the worlds biggest turd"
Darnell "Damn I aint looking at that shit you're sick"
Harold "It's pretty gnarsty I tell you