Riff Raff -- Round Two ... Bodyguards Obliterate Another Ballsy Fan

Riff Raff's bodyguards threw another gutsy fan a clue to staying offstage ... by violently throwing him back into the crowd like a rag doll.

Riff Raff was at Elektricty in Pontiac, MI on Saturday night, when an overexcited fan jumped onstage and laid hands on the man, a huge no-no that Riff's GIANT bodyguard quickly fixed.

It's no secret ... Riff's crew has the green light to manhandle dudes who jump onstage like it's street league football ... but chicks with jugs are still free to bounce.

The guy they pummeled -- Adam -- says he knew a beatdown was coming, but even though security dragged him out by his neck, leaving him battered and bruised, he doesn't plan to sue.