Police have charged a 31-year-old man with indecent exposure after allegedly flashing his genitals at two teens on a train.
He was part a group of men dressed as the Four Square man and believed to be heading to the Auckland Darts Masters.
However the group, "fuelled by homophobia and alcohol" allegedly assaulted the youths.
Jen de Montalk, the mother of one of the teens, says one of the masked men flashed his genitalia while another launched a vicious attack on her daughter's friend.
"One of them exposed himself and one of them choked the boy after calling him a f****t," she said.
"My daughter got clipped by a stray punch and the strangler also head-butted the boy. They also stole the boy's phone but the kids got it back.
"After the assault, my daughter managed to persuade one of the train staff to kick them off. They got off at the Baldwin St station."
Ms De Montalk says despite the violence and obvious intoxication of the men dressed in Four Square costumes, fellow commuters and train staffers failed to offer help to the teens.
"No one helped the kids fight them off, including two train staff who were there, but people were filming it," she said.
"This was a serious assault on a pair of 15-year-olds, fuelled by alcohol. Shame on Auckland Transport and shame on those who sat by and did nothing."
The man will appear in the Auckland District Court in September. Police say they are still investigating the matter and are not ruling out further charges.