When it comes to celebrations, Josh Naylor is unmatched ... 'cause for the second time this season, he lost his mind after a walk-off HR -- this time headbutting his own manager!!!
Naylor -- who previously went bananas after hitting a game-winning dinger back in May -- stepped to the plate in the bottom of the 10th inning with the Guardians trailing 6-5 on Wednesday night ... and then went oppo off Twins pitcher Jharel Cotton to win the game for Cleveland.
As he was rounding the bases, he got rid of his helmet -- which his manager, Terry Francona, appeared to pick up and put on -- and then he went crazy with his teammates.