Luke was seen chatting on the live feeds early Wednesday morning with contestants Jared, Cory, and Hisam when he said, "We were in the f****** (inaudible) room, n****." Realizing his mistake immediately, Luke tries to correct himself by saying "dude" ... and laughs it off.

Cory and Hisam immediately tense up, and rightfully so ... Luke looks over to Jared, who's Black, before apologizing. It seemed to tick off Cory and Hisam, who definitely didn't laugh with him -- instead, they step out, leaving Luke alone with Jared.

Surprisingly, Jared doesn't seem all that concerned with the apparent slip-up -- it's possible he wanted to keep his cool for gameplay purposes -- later telling Luke, "I don't give a f***," in response to the slur.

White folks dropping the N-word on 'BB' has become a reoccurring theme ... it's happened quite a bit over the years, especially in 2018 when houseguest Kaitlyn said it while quoting Drake's "0 to 100."

BTW, producers just warned the cast about their language after 2 contestants were worried their tans would make them look "ghetto."

CBS has threatened to kick people off the show for situations just like Luke's ... but it's unclear if he'll be forced to pack his bags anytime soon.