John Beilein's brief stint as Cleveland Cavs head coach was nothing short of a dumpster fire ... and it got so bad, the players trolled the dude by referencing his infamous "thugs" comment with the locker room music.
The 67-year-old's NBA career came to a screeching halt after just 54 games on Tuesday ... with Beilein leaving about $12 million in contract money on the table just to end his misery.
Now, details on his failure of a tenure with the Cavs is coming to the surface ... and it's uglier than imagined. Like, we knew it was bad.