Nick Diaz lived up to his bad boy reputation at today’s UFC 137 weigh-ins when he clashed heads with his opponent BJ Penn during the traditional staredown in front of a roaring crowd in Las Vegas.

The staredown started innocently enough, but then the taller Diaz ducked down and appeared to clash heads with Penn before being quickly separated by Dana White and dragged away by their corners.

Diaz then tried to exit the stage but was told to stay in order to be interviewed by Joe Rogan. Diaz was in no mood to stick around however and left leaving an annoyed looking Penn to say, “It’s time to fight.”

The flare up between them was somewhat surprising given that they have both been very respectful to each other in the build-up to the fight, with Diaz going as far as to claim that Penn is his favorite fighter.

Both men are at their best when they are fired up though, so for the fans this explosive moment was an indicator that we might be in for something special tomorrow night.

Check out how it all went down for yourselves in the video below.

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Ross launched MMA Insight (previously in 2009 as a way to channel his passion for the sport of mixed martial arts. He's since penned countless news stories and live fight reports along with dozens of feature articles as the lead writer for the site, reaching millions of fans in the process.