The chaos broke out on Tuesday ... when the two internet stars butted heads over failing to defeat the Ender Dragon. For those who have no idea what that sentence just meant, Speed and Cenat are attempting to complete a game without being able to re-spawn -- so every time they make a costly mistake, they start from the beginning.

Speed and Cenat -- who are living together for the challenge -- aren't quitting until they reach their goal ... and the cameras are rolling the entire time.

As their struggles continued, things took a turn on Tuesday ... when Kai, 22, got really pissed off and jumped into Speed's face.

Speed advised Cenat to calm down ... but Cenat did the opposite and started trash talkin' the 19-year-old.

"Back the f*** up!" Cenat said. "Ain't nobody scared of you! Shut yo Black ass up!"

They then got into an intense, UFC-esque match ... and Speed forcefully tossed Kai onto the bed to make him stop.

"Chill Kai, you can't do it to me, Kai. Just stop," Speed said. "Stop! I don't wanna go that far."

"You'll get embarrassed. I wasn't even trying!"

Mind you, these two were showering together just one day ago ... enjoying each other's company as they washed up and prepared to give the game another shot.

The viewers went nuts after the little scuffle ... but everything seems to be alright now, 'cause they went right back to playing Minecraft in front of their 100K+ viewers.