But a short conversation with the Romanian-born 24-year-old makes it clear his message is positive and from the heart.
The words tattooed on Mr Onc’s face, head and neck are eye-catching: "another beautiful day", his first face tattoo, on his forehead, beneath "watch your thoughts" in large italics, circling his shaven head, almost like a monk’s tonsure.
Below his right eye, a clearly defined "look within" contrasts with a vertical "un-comfort" running from above the left eye down his cheek but divided by the eyebrow.
"$O$" (save our souls, in dollar signs), over his left cheekbone, contrasts with a single penguin - "the one who tests the water for the rest of the group to check for sharks".
And the word FREEDOM is highly visible around his neck. Mr Onc is travelling the country, "and then the world", with his German girlfriend Elena Engelharet (also 24), speaking at as many secondary schools as possible and making positive videos for YouTube, to motivate and inspire young people.
The couple are supporting themselves by selling T-shirts and hoodies on which they have screenprinted the message "another beautiful day", which is also the name of the YouTube channel people can follow them on.
He goes to schools unannounced - "they get a shock when they see me" - and tells them about himself and his mission, so they can decide if they want him to address the pupils. The seven or eight schools he had visited in the past two weeks had received him well. Only one, in Invercargill, decided his message was not wanted.
In Dunedin, he spoke at John McGlashan College twice, a successful address to year 10 pupils on Thursday resulting in an invitation to speak to senior pupils yesterday.
The response was again positive, although the boys were probably "more focused on the tattoos", he told the Otago Daily Times, but with an appointment at King’s High on Monday, he was encouraged John McGlashan was more than happy to be a reference for him.
His message is "it doesn’t matter what you look like. You don’t have to impress people. Look within yourself. Respect each other. Don’t give up on dreams".
He saw social media as useful but thought its messages could also be destructive, so stopped using it for a time. Now he was using it again, "for a different purpose, to educate people, so they won’t make the mistakes I made".
He believed the new generation was being misled by "lost role models" and he pointed to musicians, especially rappers, whose messages were often negative and violent, with "wrong imagery" involving gangs, guns, drugs and a demeaning depiction of females. He wanted to take that rapper image and "flip it".
Mr Onc came to New Zealand with his family when he was 11. After two years in Christchurch the family moved to Auckland, where he attended St Peter’s College.
He "dropped out" at 17, having developed depression because of back injuries caused by trying to lift weights that were much too heavy for a teenage boy. As a youth, he was a very good football player and hoped to become professional, so he "overdid it. I was always trying to impress others". His English was not good and he tried to gain approval through his sporting ability.
By the age of 18, he began using alcohol and drugs, because "that was the message in the media". At 21, he decided to run away from his problems and went to Australia. There he was arrested three times and collected minor convictions for bad behaviour.
Then "it all changed". He left behind his bad associates, stopped using alcohol and drugs, and focused on "being the best I could be, every day".
Calling himself one of not many young men "spreading the love", he said his mission was to "inspire and motivate teenagers and young adults to make wise decisions, stay on the right path and never give up on dreams".
