Lil Nas X jokingly said he had a new song coming out with Boosie Badazz -- but the latter didn't think it was funny ... and hurled every homophobic slur he could at the guy.

The Louisiana rapper unloaded on LNX Saturday with an expletive-laden diatribe that's shocking -- calling Nas X the f-slur, among other things ... while also telling the 'Montero' artist that he should kill himself.

Boosie writes, "STOP TROLLING ME F***** LOL 📷U A WHOLE BITCH PLAYING WITH A GANGSTA SMH U CAN KEEP SUCKING D*** N GETTIN F***** N YOUR ASS."

As if the horrendous homophobia wasn't enough, he continued ranting and telling Nas X to kill himself, claiming he'd be doing the world a favor if he did so.

Yeah, we know ... it's wild, and about as unhinged as we've ever seen Boosie on this topic.

The hate speech comes on the heels of an IG video Nas X made, where he claimed he had a new collab coming out with Boosie ... obviously, a troll comment, as everyone knows Boosie would likely never agree to something like that ... based on his well-documented history.

Lil Nas X doesn't appear to have responded to Boosie's rant just yet -- but something tells us he'll have something to say. This one just goes way too far not to address.