all joking aside, contact paypal and tell them the whole story, paypal might send the kid a bill, and prosecute if he doesnt pay up.
if that doesnt work, contact the kids parents, and threaten to file suit if they don't pay for their idiot child's debt. They will likely settle for sending you your $100 back, and possibly more if you claim that your lost skiing time qualifies as "damages".
then buy a pair of boots, go skiing, and get on with your life.