That's St. Louis Cardinals manager Mike Shildt GOING OFF in a spectacular f-bomb-laced locker room speech after his team upset the Braves -- and it's AWESOME!!

"Now, I don't give a f**k who we play. We're gonna f**k them up!"

Atlanta and St. Louis had a chippy NLDS ... and after the Redbirds closed it out 13-1 in Game 5 Wednesday -- Shildt broke out all the cuss words!

"They started some s**t. We finished the s**t," Shildt says in the vid captured by St. Louis outfielder Randy Arozarena. "And, that's how we roll."

Arozarena apologized for posting the footage because it was supposed to be a private moment, but it was still awesome to watch.

"We're gonna take it right to them the whole f**king way. We're gonna kick their f**king ass!"

By the way, "they" is now the Washington Nationals. The two squads are set to face off in the NLCS, a best of 7 series.

As for Shildt, he's known for being a super nice and calm dude -- remember how awesome he was to TMZ Sports when we got him out in NYC earlier this year???

But, clearly, he's got a fiery side ... 'cause his locker room speech was EPIC!!!

As for why he was so jacked up ... St. Louis was pissed off at Braves star Ronald Acuna Jr. all series long for his antics at the dish (there were bat flipping and base-running dancing).