UFC superstars Daniel Cormier and Dominick Cruz -- who made a living off being fearless and smashing faces in the Octagon -- are in their feels over comments made about each other's commentating skills ... and the whole thing is incredibly petty.

Of course, Cruz recently blasted DC's fighting analysis at UFC 269 media day ... saying he mutes the TV when Cormier is on the mic, claiming he doesn't do his homework or watch enough film.

DC confronted the Dominator in a one-on-one sit-down on his YouTube channel Wednesday night ... calling out his fellow fighter for making the comments in public, instead of in private.

"You say so many things privately that I would never say publicly," DC said. "You and I say things privately that we would never say publicly."

Cruz responded by saying there's no "rule" against what he said ... claiming it was meant to hold him accountable and be taken as constructive criticism.

As for how much film DC watches, he admits he doesn't take as much time as Cruz does when preparing to call a fight ... but adamantly denies not being prepared to provide commentary.

But, the criticism wasn't one-sided -- when Cruz asked DC to share his own thoughts, Cormier said he felt Dominick's analysis can be a bit dry.

DC even goes as far as to say Cruz was "wrong" to make the comments in public ... adding, "As a colleague, a professional courtesy, you don't do that to your teammates. You don't go publicly. Those things you don't say in the public."

Overall, both guys make it clear they're still cool despite the beef ... which means the whole thing was pretty trite.