WWE’s WrestleMania Kickoff was nothing short of bonkers … with The Rockstraight-up slapping Cody Rhodes in the face in a wild on-stage confrontation!!

The whole event went down in Las Vegas on Thursday … with Roman Reignsaddressing the crowd and announcing he will face off against Dwayne Johnson in Philadelphia — claiming it’s his decision and there’s nothing Cody can do about it.

Rock then showed up and hopped on the mic … saying no matter what people think of the controversial matchup, they WILL respect it — as Rock and Roman come from The Bloodline, the Samoan families with the richest history in professional wrestling.

Everything seemed set in stone as both guys shook hands — but Cody wasn’t having it … taking the stage and calling the whole thing “bulls***,” as he won the Royal Rumble and earned the right to enter the squared circle with Roman.

The guys traded nasty insults about each other’s families … and when Cody said Roman and Rock’s grandparents would be ashamed of what they have become, The People’s Champ lost it — rocking Rhodes right in the mouth.

All sides needed to be separated and escorted off the stage … but it didn’t stop there, as a livid Rock confronted WWE chief content officer Triple H afterward, telling him to do something about Rhodes’ disrespect — or he’d handle it himself.

After it all died down, the WWE apparently sided with Rhodes in the whole ordeal … revealing Cody would get his wish and take on Roman at WrestleMania 40.

Rock, meanwhile, has fully aligned himself with the Bloodline, which has wrestling fans freaking T.F. out.