A Post Office worker was left terrified after a regular customer barged behind the counter and grabbed a considerable amount of cash from the till.
Nicholas Carter, 41, was so well-known by staff that the employee present thought he was joking at first.
Carter, from Flushing, appeared at Truro Crown Court for sentence having pleaded guilty to robbery.
Prosecuting the case, Michael Green described how on February 25 at around 3:30pm Patricia Lowe was working at Penwerris Post Office in Falmouth.
She was serving another customer when she heard Carter saying he wanted money.
Ms Lowe presumed that he wanted to make a cash withdrawal.
Mr Green spoke of how Carter then walked around the side of the counter while Ms Lowe was serving another customer, entering a staff-only area and walking towards Ms Lowe.
Ms Lowe thought Carter was joking but he soon pulled out the cash drawer and started taking cash.
Carter then forcefully grabbed Ms Lowe's arm and pushed it away.
Ms Lowe described being "frightened and scared", saying his grip was hard.
It was estimated Carter took between £1,500 and £2,000.
Ms Lowe sounded the alarm and told police who Carter was and he was arrested two days later.
In her victim impact statement Ms Lowe spoke of being shaken, now being suspicious of everybody in the shop and being scared to walk to and from work.
Representing Carter, who has 14 previous convictions, Dieter Kehler said: "He moved down to Cornwall to get away from his troubles as a young man but moving down didn't remove him from his mental health issues.
In stressful situations he doesn't think as clearly as the rest of us.
"On that day he was at an extremely low point. He was homeless, was using alcohol to excess and was in a very desperate situation.
"It was an unsophisticated matter. Everyone in the post office knew who he was. It was a desperate grab for money.
"Things have now changed. He is working in a gardening and landscaping job and he recognises the problems he has to address."
Sentencing Carter, Recorder Christopher Quinlan, KC, went over the facts of the case, adding that Ms Lowe was vulnerable as she was working alone on the shop floor.
He also noted Carter's change in circumstances and attempts to get his life back on track before jailing him for 18 months.
