Kyle Rittenhouse says he's no longer a fan of LeBron James ... saying the Lakers star's shade toward him during his trial "really" ticked him off.

"I liked LeBron," the Kenosha shooter said Monday on The BlazeTV's "You Are Here" show. "And, then I'm like, 'You know what, f*** you, LeBron.'"

If you missed it ... LBJ mocked Rittenhouse after the 18-year-old gave an emotional testimony on the stand during his homicide trial last month.

Rittenhouse fought back tears while explaining how the Aug. 25, 2020 shootings in Wisconsin unfolded ... and then he got so choked up, the judge actually paused the court proceedings for several minutes.