Buehler's chug got all the festivities kicked off on Friday afternoon ... as just after the team's championship busses got going down their parade route through downtown Los Angeles, he whipped out a beer bong and guzzled a cold one.

For the next hour or so, around an estimated two million people cheered on the newly minted champs as they made their way through the roadways.

Eventually, the team ended up back at Dodger Stadium -- where Ice Cube performed a mini-concert to help welcome them to the field.

He belted out "Bow Down" -- and then as he began "It Was a Good Day," Roberts joined him onstage ... and backed it up when Cube sang, "I can make the ass drop."

Players then hopped on the microphone -- and Buehler's speech was perhaps the most memorable ... even if it was the shortest ... as he donned Orel Hershiser's old World Series jersey and screamed, "We're world f***ing champions, motherf***ers!"

Teoscar Hernandez and Clayton Kershaw also took turns speaking ... and each had tears streaming down their faces as they spoke to the thousands gathered at the ballpark.

Ohtani -- whose dog, Decoy, had been with him earlier in the day -- got on the mic, too ... and said a few sentences in English, which brought the crowd to its feet.

There was more ... Kiké Hernandez also dropped some shade on Fat Joe -- telling everyone he knew Game 3 was over as soon as the rapper finished up his pregame performance at Yankee Stadium.

Almost all of the guys said they were looking forward to running things back next year -- and with nearly every one of their superstars slated to return, it might only be around 365 more days 'til they're giving title speeches in L.A. again.