Grungy socks. Very dirty or crusty socks. Usually worn more then a day at a time.
Person 1: What is that smell?!
Person 2: I think it's zak's yellow grocks!
Combination of the words great and rocks. Is meant to denote something so exciting/awe-inspiring that not just one of those above words will suffice.
"Dude, you finally got an internet connection in your room?"
"Yeah, it fucking grocks!"