Our sports teacher in high-school would tell us to stand straight. Then he would shove us from the back a few times. The foot we would stop ourselves from falling would be our leading foot (for snowboarding). So if you catch your fall with your left foot, you're regular. Otherwise goofy. Don't know if that's a safe bet, but it seemed to work out for us back then.

OTOH: I am convinced I can't snap my fingers with my right hand and never will because my specific mix of handed-ness makes it impossible for me to do so, no matter how hard I try and practice. No problem at all with my left hand.