There were nearly 20,000 people screaming the f-word at Reggie Miller on Wednesday night ... but just in case he didn't hear it, Knicks star Josh Hart told him all about it -- repeating the obscenity to the Indiana legend on a hot mic!
The hilarious moment happened at the end of New York's playoff victory over the Pacers ... when fans at Madison Square Garden ribbed Miller, who was helping broadcast the game for TNT, with a "F*** you, Reggie" chant.
The Knicks supporters -- still clearly salty over the way the Hall of Famer tortured them during his playing days some three decades ago -- really let the former Pacers sharpshooter have it .