The scared woman ran out a back door to find help.
Poi stole $800 worth of cigarettes and took off.
In sentencing, Judge Bridget Mackintosh said Poi had been on synthetic cannabis the day he committed the crime. He was also subject to release conditions at the time. The Judge said the victim now felt uncomfortable in her work place and had trouble trusting people who entered the shop.
Poi, who was 19 at the time he offended, has "quite a history" of offending, Judge Mackintosh said.
Two years ago he was convicted for jumping on the bonnet of a police car and kicking in its windscreen outside the Napier Court House. He did this just a week after being released from prison where he was serving time for charges of wilful damage, theft, disorderly behaviour and misuse of a credit card.
Last week, Poi was also convicted and discharged on wilful damage charges.