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L.A. Clippers honcho Doc Rivers has some friendly advice for his pal Donald Trump -- STOP SCREWING WITH MEXICAN DRUG LORD EL CHAPO!!!!

FYI -- Rivers and Trump have been friends for years ... and we shot footage of the two of them leaving a business meeting together in Beverly Hills earlier this year.

So, with the news of El Chapo threatening Donald Trump for calling the escaped drug lord "everything that's wrong with Mexico" ... Rivers says D.T. better watch his back!!!

BTW, we also asked Rivers about reports that his daughter Callie Rivers was the main person who got DeAndre Jordan to back out of his Mavs deal and stay with the Clippers.

Doc calls B.S. on the whole thing -- and tells us the REAL reason Jordan decided to stick around.

Check out the clip.