Dwayne Johnson Drops Surprising R-Word in Wild Kevin Hart Roast Set

Dwayne Johnson made a not-so-shocking appearance last night at Netflix's "The Roast of Kevin Hart" ... but then went hardcore, even dropping the R-word, which, if you know his past, is wild.

The movie star was the last person to light into Kevin before it was the comic's turn to throw zingers at everyone else who'd burned him -- and DJ made it count big time.

The short-guy jokes and the quips of talentless-ness were all par for the evening's course -- and even Dwayne hitting on KH's wife was funny -- though not shocking -- but then he dropped the R-word while making fun of controversial NBAer Draymond Green.

Poking fun at his name ... Dwayne said the name Draymond is lazy -- just adding a "D" in front of Raymond, which he then called "Dret***ed." DJ then repeated the slur ... mentioning the Golden State Warriors got bounced from the playoffs -- so it's time for DG to "Dretire."

The roast was a no-holds-barred night, so it could be argued Dwayne was just playing along, but for those who know Milton Rosen -- a Special Olympics athlete who is also one of his childhood pals -- the slur was an odd choice. Their story together was even highlighted in the ESPN feature "The Rock's Rock."