Chad Johnson Busts His Ass In Hilarious Sandboarding Fail

ANOTHER ONE BITES THE DUST

Chad Johnson is a master in footwork, but his skills certainly don't translate to sandboarding ... 'cause the ex-Bengals star tried out the sport -- and straight-up busted his ass!!

The former NFL wideout is in Qatar covering the World Cup for FOX ... and during a bit of downtime between games, he decided to hit the dunes for a boarding lesson.

The tutorial seemed to go pretty well at first ... but disaster struck as Ochocinco gained momentum going down the hill.

Check out the video -- Chad loses his balance as his speed increases ... and inevitably, it resulted in eating sand.

All appears to be well, though ... and luckily for Johnson, he was able to avoid any serious…