What did Lakers player Josh Hart tell his teammate, Lonzo Ball, when he caught him listening to his OWN rap music in the gym??? 

"TURN THAT SH*T OFF!"

It's actually pretty hilarious ... Hart could hear the ZO2 joint, "Gotta Get It," bumping from across the Lakers facility on Wednesday and decided to shame his pal on social media. 

When the camera focused on Lonzo, he started dancing ... hard. 

Hart added a comment when he posted the footage on IG -- "weak ass rappers."