Mike Tyson -- Slap Boxes Jon Jones ... Wins

He's still got it.

Mike Tyson is still the champ when it comes to slap-boxing ... and Jon Jones learned that the hard way outside of WWE SummerSlam in L.A. Sunday night.

The two were goofin' around in front of Staples Center -- when the fighters squared off ... with some open-handed pugilism.

Jones handled himself pretty well ... until Mike moved to his inside and tagged the UFC superstar right on the jaw -- and even Jones admits if the brawl was full-force ... "He'd kill me."

Now that's a fight we'd LOVE to see.