Constable Dominic Gaynor admitted pointing his gun at and threatening to shoot his junior colleague, Morgan Royston, at a Sydney city-centre police station in May last year.
The 30-year-old was on duty behind the front desk of Day St police station, in Chinatown, when then-probationary constable Royston began discussing Top Gun: Maverick, which he had seen the night before.
Gaynor told him not to ruin the movie, to which the younger officer replied: "I'll spoil it for you."
According to court documents, Gaynor responded: "Don't spoil the movie, c***."
Gaynor then threatened to shoot Mr Royston before laughing and taking his Glock out of its holster.
He pointed the weapon towards the other officer for around five seconds without his finger on the trigger.
Mr Royston, who has since left NSW Police, said the incident forever changed his life and made him lose all trust and admiration he once held for the state's police force.
"My shift (that day) was initially unremarkable," he told a sentencing hearing for Gaynor at Sydney's Downing Centre Local Court on Thursday.
"I had no idea that the course of my life was about to change forever.
"Suddenly I was staring down the front of a loaded police pistol."
The former officer said he will never forget the "overwhelming shock and fear" he felt as a gun was pointed at his head.
Mr Royston described the months of anxiety and hyper-vigilance that followed, including falling into a deep depression and having regular nightmares of being shot and killed.
He said he was torn between reporting the incident and "a desire not to break the police brotherhood of dobbing on another colleague".
According to a tendered police statement, Mr Royston froze and didn't know what to do before he reported the incident to a supervising officer around a week later.
"I completely lost the trust and admiration I had for the NSW Police force," Mr Royston told the court.
"I thought I would be safe around my trained colleagues ... it's put the permanent fear of harm into my mind."
According to the NSW Police handbook, which Gaynor accepted he was aware of, police should treat all firearms as if they are loaded and be conscious of where the muzzle is pointed at all times.
He pleaded guilty to carrying a firearm in a manner likely to injure a person.
Several other charges against him were dropped, including a charge of common assault and two counts of stalking or intimidating.
Lawyer Chris Micali conceded Gaynor misused his weapon but said he was otherwise a "fantastic" member of the police force.
"This is a remorseful man who made a grievous error that will cost him dearly," he said.
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