Kevin Durant says DeMarcus Cousins is lying through his teeth -- adamantly denying the Phoenix Suns were throwing hands in the locker room this season ... right after the ex-NBA center made the shocking claim.

Boogie -- who made headlines for, ironically, fighting with fans in Puerto Rico earlier this month -- went on FanDuel TV to talk about the Suns' tumultuous 2024-25 campaign ... and said he was told the team vibes got so bad, players were fistfighting in the locker room.

Boogie was actually defending his former Warriors teammate in his appearance ... saying he wasn't at fault for the Suns' issues -- it was more so due to the fact the execs threw a bunch of scorers together and said, "go win a championship."

"There was a lot of things that happened that haven't been reported. I don't want to be the guy to report it, but I've definitely heard of some of the negative things in the locker room. There was a couple of fistfights. There was a lot going on that obviously carries over to the court."

When asked to clarify, Cousins said the brawls "absolutely" happened.

Durant got wind of Cousins' words ... and hopped on X to shut all the chatter down.

"I have to contest this 94 footer," Durant said on Friday. "This some bulls*** to throw on us. Yea yea yea we were trash this year ha ha ha but we NEVER got close to this. NEVER."