"She said, 'I could ask you the same thing, you should go back to your country.' I was kind of shocked because I'm born in Sydney and that's when the video happened."
Mr Forbes then filmed the rest of the conversation, showing only his face.
The woman can be heard telling him she did not believe him when he told her he was born in Australia, and, when she learned his father was foreign-born, told him he should "pack up and return to New Zealand".
Mr Forbes' father Jason posted the video to YouTube on Tuesday and it quickly went viral, with Jerome garnering widespread praise for his calm response to the woman's bigoted attack on him.
By this morning, less than 48 hours after it was posted, it had 1.6 million views and more than 10,000 comments.
Mr Forbes and his father had been fielding interview requests from across Australia and the United States.
The 20-year-old said he could never have anticipated the response.
"I think I was so calm because I served a mission for my church, a Mormon church, in Port Macquarie, and I came back and that taught me patience," he said.
"I just built up a tolerance to people having a go at me. I've learnt that they are not having a go at me in general and she was having a go at foreigners and not me personally.
"I feel sorry for her, for her ignorance, I guess, it seemed she had a really small perspective on life. It's sort of sad that's what she still thinks at her age."
Mr Forbes can be heard unsuccessfully attempting to reason with the woman over her views.
He said the woman was about 70 years old.
"I wasn't taking it as a personal attack because a lot of the older generation are brought up sort of racist," he said.
"I just thought it was funny because she told me to go back to my own country when I was born in Sydney, so I recorded it."
