The earliest instance I found in print is Desmond Muirhead's 1962 Surfing in Hawaii: a personal memoir: Then he turns and surfs right-foot forward (goofy stance) towards the left, again so his body is facing us. The third time is (more) successful: first he surfs left-foot forward (regular stance) towards the right, so his body is facing us. The first two are unsuccessful and he can't stand up on the board. In fact, after watching the 1937 Disney animation Hawaiian Holiday, Goofy surfs with whichever foot forward makes him face us. I agree with FumbleFingers: it's likely both the surfing term and Disney's Goofy character comes from the earlier goofy meaning of stupid, silly, daft. The original terms goofy-foot and goofy-footers (later shortened to goofy) appear to have become popular in surfing during the early sixties.