Words and things, mostly words.
In typical fashion, UFC President Dana White claimed that he’d booked fighter — in this case one Nick Diaz — in a bout that had actually not been agreed upon. This is a common tactic used by the promoter, to then leverage fan pressure on the fighters to force match-ups they want — at price-points they want. It’s often effective, as it also gives the UFC the out to say the fighter was being difficult for whatever reason they want — and fans love any opportunity to criticise a non-compliant fighter. This is easily enabled by a generally useless MMA media which by-and-large does little more than repeat UFC statements.
I don’t even know why the UFC would try this with Nick, however. Just like his brother Nate, the elder Diaz has no issues ignoring whatever the promotion wants. Telling a Diaz brother what to do is the most assured way to ensure you get the exact opposite response. The UFC must be desperate for star power, as this whole situation will do nothing for either side, but Nick Diaz clearly doesn’t need to fight.
Nick gave a response to Dana White’s claim which can be read here. It appears they are the ones who are “tripping.”