Popularised by the legendary snowboarder JP Walker. Sick Son is a compound word that directly adresses the person you are speaking to "son", and describes to them how good something was "sick". Usually followed by "uuuuuugh" or "uuuurr" or however one would spell it.
"Hey just got down to Cali. Copped the bends real quick. Swooped up a couple of new surf boards. Gunna head down the beach, maybe get a barrel. It's gunna be SICK SON uuuuuuuuurgh."