Reihana Adam Tahau came across the officer, who he had had previous dealings with, in Pak'nSave in Whanganui on July 21. The officer's children, aged 7 and 9, were with him and Tahau had his own children with him.
The Whanganui District Court heard the police officer considered the man "accosted" him and wanted to "go outside" but the defendant said he just wanted to talk.
After walking past the victim, Tahau returned and stood with his trolley in the way, police prosecutor Sergeant Stephen Butler told the court on Tuesday.
The victim walked to another area and Tahau followed, and began confronting the officer about an incident in 2014.
Butler said Tahau "said the victim was not so tough without his uniform on".
Tahau positioned his trolley to get into the victim's way again, and "said to the victim to go somewhere else and that he was not afraid".
He blocked the victim with his trolley three more times, then began walking alongside him.
"He said, 'Do you know what I've been to jail for?'. He continued to tell the victim he's not afraid of going to prison."
The victim was eventually able to continue his shopping trip and leave.
When spoken to by police, Tahau said he "just wanted to talk man to man".
He pleaded guilty to intimidation.
Defence lawyer Stephanie Burlace said Tahau had not intended to be intimidating, but realised in hindsight how his actions could be seen as such.
She said the victim had nodded at Tahau and Tahau took it as an invitation to approach him.
"He did raise the incident in 2014. He had some grievances and was quite passionate about what happened," Burlace said.
"He even said to the officer he could see he was shaking a little and said words to the effect of 'You don't need to be scared, I just want to talk to you about it'."
She said Tahau had his own two children with him at the time as well.
"He accepts he might look intimidating to some people.
"If the officer had simply said to him, 'Look, I really don't want to talk about it in the middle of a supermarket in front of my kids, come and see me at work', he would have done that. He thought he could have this chat person to person."
Butler called the incident a "deliberate accosting of an off duty officer while he was trying to do his shopping with his children".
Butler said the victim "wasn't scared".
"It was the fact that he was with his children. Mr Tahau was following him, trying to intimidate him, trying to take him outside to have a one-on-one confrontation, so to speak."
Judge Philip Crayton said those in public service had a right to go about their personal life without being disturbed.
"However strong your feelings are, there is a time and there is a place, and this was neither," he said.
He sentenced Tahau to 130 hours of community work and made a non-association order between Tahau and the victim.
