Derived from a "voluntary fall"
Meaning after after attempting a wicked cool stunt, you screw up, and start to fall, and try to make it look like it is completely voluntary, but everyone knows its not.
"LOL DID YOU SEE JOE? THAT WAS SOME FALLUNTARY SHIZNIT!"
"Icy Hot Stunta tried to do a backflip, but he biffed falluntarily on his face"