British White Guy K.O.’d …AFTER RACIST RANT IN LONDON TRAIN

Check out this one-hitter-quitter that went down over the weekend on a train in the London Underground metro system, where this white guy was mouthing off to three Black youths … for no apparent reason. He starts out as simply bigoted, but eventually turns full racist.

Watch … the man’s going off about this being “my home” in an incoherent tirade. He’s arguing with the one guys off-screen, who’s asking what his name is and where he’s getting off. Soon, the instigator brings up race, saying with derision … “You’re black.”

People around him ask what that has to do with anything, and he shooshes them … firing back, “This is popular.” You can tell he’s getting a kick out of riling everyone up too.

The video then cuts to the three Black dudes getting off at their stop, and as they pass the white man — who’s got his fists balled up, ready to fight — one the young’ns swings on him and connects with his jaw, sending the guy flying back and landing hard on the ground.

He’s out cold, staring off into space as people say he deserved it … before a couple of people start helping him. Police say they’re aware of the incident and are investigating. (TMZ).