A brief embrace, a case of mistaken identity and suspicions of infidelity prompted a drunken one-punch that shattered a man's jaw at a Civic nightclub in the early hours of the morning.
The impulsive blow broke the victim's jaw in two places and left the victim in "agony". Doctors had to insert six screws and two plates to fix the damage.
Ryan Anthony Myles had knocked back more than a dozen beers in the hours before he arrived at Academy on Bunda Street with his then-partner and three friends on October 23 in 2016.
The couple were walking downstairs to the club's main dance floor when his girlfriend had greeted the victim and leaned over to give him a quick hug about 2am.
Myles, then aged 23, soon formed the belief the man was his girlfriend's ex-partner and she had cheated on him.
He clenched his fist and swiftly punched the man in the jaw. The man managed to remain on his feet, but he was taken to Canberra Hospital and later had surgery.
Myles pleaded guilty in the ACT Magistrates Court to recklessly inflicting grievous bodily harm.
In sentencing remarks published on Tuesday, ACT Supreme Court Chief Justice Helen Murrell said Myles deliberately delivered the "unanticipated, unprovoked and strong punch" to the man's face.
The attack was impulsive and not premeditated, she said, but a blow to the face was "an obviously dangerous act".
"The fact that the offence was committed under the influence of alcohol is no excuse whatsoever.
"The potential for alcohol to cause immature young people to engage in violence is notorious."
Chief Justice Murrell acknowledged the victim's "serious injury" - although she said he was lucky and the injury could have been much worse - and ongoing psychological problems, including anxiety.
She noted Myles had accepted full responsibility for his actions and expressed remorse and empathy for the man.
The judge said referees described Myles' outburst that night as "out-of-character" and the "respectful and courteous" offender didn't usually resort to violence to resolve conflicts.
"They confirmed that the offender is very remorseful about the offence, guilty about the impact on the victim and ashamed of letting down his own family," she said.
The incident had cost Myles his girlfriend, who he had since split with, and made him realise he was an alcoholic after years of binge drinking.
Chief Justice Murrell accepted Myles had a limited criminal history, excellent prospects for rehabilitation and had made good progress with treatment for his addiction.
But she said the community was gravely concerned about the prevalence of alcohol-fuelled one-punch attacks by young men, and there was a strong need for general deterrence.
"Such attacks may devastate the lives of victims, and they impact on the ability of other young people to confidently enjoy public socialising."
She sentenced Myles to one year and 10 months' imprisonment to be served in the community under an intensive corrections order. It will target alcohol consumption and anger management.
He was also ordered to complete 249 hours of community service work.