A singer "saw red" on the night his town centre bar was closing down and thrust a broken bottle into a man's head.
A court heard Steven Harwood-Brown threw one of his employees to the floor at Folkestone venue Picklebacks, before stabbing Hossein Haderbashlu, who had intervened to stop the fight.
The dad-of-two, drunk and bare-chested, had been in a "terrible emotional state" and "lashed out", leaving Mr Haderbashlu badly wounded.
Harwood-Brown was arrested and bailed - and over the past year has been singing at local bars and charity events.
But last week the 32-year-old was jailed for three years at Canterbury Crown Court.
Prosecutor Ben Wild described how the violence erupted at Picklebacks in the early hours of August 18 last year.
He told how Emirkan Karatas, a friend of Mr Haderbashlu, had been working behind the bar with Harwood-Brown's partner, Holly Haestier.
He said: "The pair can be seen flirting with each other on the bar's CCTV a little after 4am while cashing up. The bar is closed to the public.
"Mr Karatas appears to continue to flirt with and touch Ms Haestier, who refuses his advances."
In security footage shown during the hearing, a shirtless Harwood-Brown can be seen speaking to Ms Haestier before confronting Mr Karatas.
"Mr Harwood-Brown grabs Mr Karatas and throws him to the floor, kicking him and striking him with a bottle," continued the prosecutor.
"The bottle is taken off him by Ms Haestier but he appears to continue to strike Mr Karatas who is on the floor."
The court heard it was around this time that Mr Haderbashlu entered the now closed bar in Cheriton Place and tried to break up the fight.
Mr Wild told how the victim heard Harwood-Brown shouting "I want to kill you" before pulling the attacker off his friend.
The prosecutor said: "Mr Haderbashlu has his hands on Mr Harwood-Brown's shoulders from the front, slowly walking him away when Mr Harwood-Brown shoves him away.
"He then grabs the glass bottle from earlier, smashes it on the bar and shoves it into Mr Haderbashlu's head area."
The 38-year-old was left with a gash to his left ear, which needed eight stitches, and a deep wound to his left hand, which required a further seven.
Mr Haderbashlu said in a victim impact statement: "I'm a father, educated, I've never been in a fight and I try to keep away from bad behaviour.
"My mind goes back to that night a million times a day. I still have a lot of pain in my head, my thumb is 40% numb and I find it hard to do the basic things with it.
"I knew it was my responsibility to report it. I worried what the guy might do next time if I didn't."
Harwood-Brown was arrested and gave a no-comment police interview before pleading guilty to causing grievous bodily harm with intent at a case management hearing in August this year.
Supported by friends and family in the public gallery on Friday, he attended court wearing a black suit and remained silent throughout proceedings.
The court heard he had three prior convictions - for resisting a constable, assault occasioning actual bodily harm and violent disorder.
However, Adrian Rohard, mitigating, argued that Harwood-Brown was now a changed man.
"He has spent the last year working on himself to correct his path, to change his outlook and address some of the issues that were prevailing at the time," said Mr Rohard.
"The context is that Mr Harwood-Brown was closing down that business on the night this occurred - he was in a terrible emotional state.
"Before all this happened, he had been crying in the office upstairs saying, 'I don't know if I can go through with this and let all the staff down'.
"He had borrowed money from friends and family and while, on the face of it, the business looked like it was a success, the numbers were not adding up."
Mr Rohard said his client's intoxication was to cope with the stress of Picklebacks' closure and that the attack was a spontaneous, emotional reaction to protect his girlfriend.
He said: "Mr Harwood-Brown remembers saying to Holly, 'Is he causing you a problem?' and she was quietly indicating that that was the case.
"Those were the impulsive circumstances in which this occurred.
"Mr Karatas' friend then comes in, and in that moment, he just saw two men in front of him.
"Whether he felt mistakenly threatened, he just saw red and ended up lashing out at the victim in this case, who had nothing to do with Mr Harwood-Brown in this situation."
The lawyer said that since the incident, Harwood-Brown has become more "community-minded", working as a singer to raise money for charity.
He urged the judge to consider handing down a suspended sentence, highlighting the effect an immediate custodial term would have on his children.
But Recorder David Blundell KC told Harwood-Brown the attack was so serious that immediate imprisonment was the only appropriate punishment.
"Your character reference letters speak to how out-of-character this attack was for you," he said.
"But using a smashed bottle and shoving it into Mr Haderbashlu's head and neck area amounted to the use of a highly dangerous weapon.
"The custody threshold is clearly passed."
Harwood-Brown, of The Meade, Hawkinge, was given a custodial term of three years.
He will be released no later than halfway through his sentence for the remainder to be served on licence in the community.