UFC fighter Anthony Smith HATES Luke Rockhold's guts. Like REALLY hates him.

And, moments ago, Smith issued a threat to Rockhold, despite the fact they don't even have a fight on the books.

"That guy’s a f*cking piece of sh*t," Smith said at the UFC press conference in Atlanta moments ago.

"F*ck Luke Rockhold."

So, why the hostility?

It stems back to a radio interview Rockhold did earlier this year when he called Smith a "sloppy bum" who wasn't worthy of a fight with Jon Jones at UFC 235.

Smith was clearly offended -- and used his opportunity Friday to lash back at Rockhold.

"The first opportunity I get I’m gonna drill a hole through Luke Rockhold’s f*cking face. I promise you guys that.”

“The first opportunity I get after this fight, doesn’t matter what happens. I’ll fight Luke Rockhold on one f*cking leg. I’m gonna beat that dude's f*cking ass.”