When it comes to trash talk, mothers are off limits. Nobody told that to Matt Barnes, though. 

In the heat of the battle of Game 2 of the Los Angeles Clippers-Houston Rockets playoff series Wednesday night, Barnes made a profane remark to James Harden's mother.

The Rockets' star's older brother didn't appreciate that from the Clippers' small forward. So, he made Barnes apologize. 

"My older son walked over to him and told him to apologize," Harden's mom, Monja Willis, told TMZ Sports. "And he did. What he told me was that he would never want to disrespect anyone's mother because his mother passed from cancer...and that he was sorry. I accept his apology."

Yeah, sometimes big brother has to intervene...especially when it comes to blatant disrespect.

Rockets coach Kevin McHale couldn't believe it upon hearing about the story. 

"You don't say anything to [the mother]," McHale told ESPN about the unwritten rules of thrash talking in the NBA. "If you got something to say, say it to the guy you're playing against. I never thought of talking bad to Magic [Johnson's] mother. It's hard enough talking trash to Magic."

Out of bounds, Matt.

Game 3 of the Clippers-Rockets series is Friday night in Los Angeles.

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(Photo: FREDERIC J. BROWN/AFP/Getty Images)