UFC star Fabricio Werdum attacked another UFC fighter with a boomerang in Australia.
Seriously -- we're not making this up.
It all went down at the UFC fighters' hotel in Sydney ... when rising welterweight star Colby Covington allegedly called Werdum a "filthy Brazilian" in the lobby.
FYI, Covington hurled a similar insult at a Brazilian crowd after his last fight in Sao Paulo ... and Fabricio's one of the UFC's biggest Brazilian stars.
So, Werdum did what any angry Australian tourist would do -- he took it outside and UNCORKED HIS DAMN BOOMERANG!!!
Later on, Covington recorded himself going on a racist and homophobic rant against the former heavyweight champ ... where he claimed Fabricio also punched him in the face.
"Look at you, f**king f**got," Colby said. "F**k Brazil. F**k Fabricio Werdum ... and they wonder why they get talked to like that -- 'cause they’re a bunch of animals."
But Werdum says he didn't punch Covington ... claiming Colby got physical first by throwing a kick.
The UFC released a statement saying they'll investigate the incident. Covington told MMA Fighting he plans on pressing charges.