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“This is a disgusting display of abuse which quite frankly has no place in society,” Chief Inspector Gareth Parkin said in a statement. “All hate incidents are treated with the upmost severity and this behavior will not be tolerated in Greater Manchester.”
Witness Nick Spragg told NBC News most of the passengers were on the vet's side.
"The only good part of the whole thing was the guy on the tram then being congratulated for sticking up for himself and getting a round of applause off most of the commuters on there," he said.
The tirade on the tram erupted after the vet told the beer-swilling trio to stop swearing in front of children.
“Don’t chat s--t when you’re not even from England, you little f-----g immigrant,” one of them yelled, calling the vet a "muppet."
"You’re a dirty little immigrant," he added. "Get back to Africa!”
The vet fired back, “How old are you? I’ve been here longer than you.”
And as the teens continued to harangue him, the vet kept his cool. “You are extremely ignorant," he said. "You’re not very intelligent, do you know that?”
At that point, two of the loudmouths could be seen pushing up to the vet. One of them snarled: “Hey, you jump off the tram now, bro, and I’ll take you off the tram now” while the other tossed what appeared to be a spray of beer from a bottle at him.
Suddenly there were screams. “There’s a baby there,” one woman cried out. “There’s no need for that. There’s absolutely no need for that.”
His T-shirt drenched, the vet started to go after the teens who by then had gotten off the tram.
“Seven years in the military, I would…” the vet said, his last words unintelligible over the noise.
“It’s not worth it. It’s not worth it,” an outraged woman said while others on the tram yelled, “Disgusting! Disgusting!”
“To England, you’re a disgrace,” a tram passenger yelled at the threesome.
Corky Siemaszko is a senior writer for NBC News Digital.