Labourer Cameron Richard Fleming (21) and apprentice boat builder Joshua Richard Cunningham (22) pleaded guilty to aggravated robbery and avoided jail only because of the "unusual circumstances", Judge John Macdonald said.
On March 19, the defendants were out drinking in the CBD.
At 3.30am, they decided to call it a night and began walking to their vehicle in Filleul St.
On the way, they saw the victim and offered him a ride back to his home in the north of the city.
But they made an unscheduled stop at Prospect Park. Fleming’s counsel Brian Kilkelly called what happened next "a drunken escapade which had very, very little forethought".
Cunningham popped the boot while his co-defendant covered his face with a bandanna and grabbed the replica AK-47.
It contained $140 in cash and some bank cards.
The defendants drove off, leaving the victim at the park but it took little police work to track them down as the man knew the robbers and had seen Fleming’s face before he covered it.
"The lack of sophistication was quite clear," Mr Kilkelly said.
The use of the bandanna, he said, spoke to just how brainless the endeavour was.
Judge Macdonald said there was no physical impact on the victim but he found it a frightening experience.
"I don’t want young people to go to prison when they have done a silly thing for the first time," the victim wrote in a statement.
The judge called his stance "exceedingly generous".
During interviews with Probation, the defendants each admitted they had been intoxicated at the time of the offending.
While that was no excuse, Judge Macdonald said, "I very much doubt this would have happened if you had been sober".
Both men were assessed as a low risk of reoffending.
Fleming and Cunningham were sentenced to nine months’ home detention, 200 hours’ community work and each ordered to pay the victim $850.
The judge made an order for the fake firearm to be forfeited.