Similar to blue balls, "blue feet" is the feeling a skateboarder gets when either they come across a perfect skatespot while not having their board handy, or for any other reason are unable to skate when they are dying to.
This term can also apply to any kind of board rider or foot-focused athlete for that matter.
"Yo peep that buttery hubba ledge across the street."
"Wow its perfect. We shoulda brought our boards.. didn't know there'd be spots around here.."
"Ah.. you feelin the instant blue feet right now? Im in pain.."