Tutengaehe walked in to his local Gayhurst Rd shop earlier in the day, bought a 2 litre bottle of milk and asked the shop owner when he closed that night.
When the shop shut at 8pm, the dairy owner walked to his car with a backpack containing the day's takings.
As he got into his car and sat down to drive home, Tutengaehe opened the driver's door and stabbed the man in his shoulder with a 30cm knife.
He demanded the backpack, but when he stepped back, the dairy owner shut his car door and tried to drive off.
The youth smashed the car window with his elbow before stabbing the man "four or five more times" in the upper right arm. The victim received four puncture wounds to his right arm and shoulder.
He managed to drive off, as Tutengaehe tried to cling to the car, and get to hospital where he received stitches.
Judge Kellar today said the physical injuries were not as bad as they could have been.
But the 30-year old dairy owner, who had been struggling to operate in the badly quake-damaged suburb of Dallington, had suffered "quite significant emotional trauma" after the attack.
"One can only feel deeply sorry for the victim," Judge Kellar said.
Tutengaehe, also known as Whaanga, belonged to the local Crips gang which the judge said operates a "culture of violence".
On May 11, he was driving along Cashel St in Christchurch with five others, when they stopped to approach two men who had bought some bourbon and cola from a liquor store.
The two men, aged 18 and 20, were punched in the face repeatedly by the attackers, including Tutengaehe, and robbed of their alcohol.
Tutengaehe's family were in court and told him they loved him as he was led to the cells.
