Theodore Derrick-Hardie was just 17 when he pulled out a knife and stabbed Warren Rosillo at a birthday party last year.
Derrick-Hardie had initially pleaded not guilty to murder but changed his plea on the morning of his High Court trial in July.
Justice Edwin Wylie told the High Court at Auckland this morning the courts had to respond sternly to young people who chose to carry knives.
"You distinguished yourself as being a dangerous and menacing member of society."
Justice Wylie gave the teen some time off his sentence due to his age and described him as immature.
The court heard Derrick-Hardie carried knives in the months leading up to the killing and discussed stabbing people on Facebook.
On July 29 last year he and his ex-girlfriend were at a birthday party in the east Auckland suburb of Pakuranga.
According to the police summary of facts, Derrick-Hardie's ex had been flirting and talking with Mr Rosillo before Derrick-Hardie asked her to leave with him.
They went to the front of the property where an argument broke out. Crown prosecutor Warren Cathcart said Mr Rosillo stepped in.
Derrick-Hardie accused his ex-girlfriend of being unfaithful. She responded by kissing Mr Rosillo, who returned the kiss.
Derrick-Hardie grabbed Mr Rosillo by the neck, and stabbed him in the chest, face and abdomen.
Mr Rosillo died at the scene.
Derrick-Hardie went on the run but was arrested the next day at the Heritage Hotel in downtown Auckland.
- Edward Gay, APNZ court reporter
