Connor Doughton, 16, went berserk after being escorted back to his parents' house in Blackwood, Caerphilly county, by two men who were trying to stop him getting into trouble.
Michael Lee Emmett, 29, was stabbed in the liver in the attack in August 2014.
Doughton, who knew his victim, admitted murder at Cardiff Crown Court and was handed a life sentence.
The court heard that shortly before the attack, an intoxicated Doughton had been trying to fight a bouncer.
He had been smoking outside the Stonehouse pub in Cefn Fforest and had also been abusive to a woman in the street.
Once home, he went to the kitchen to grab a knife before running back outside and stabbing Mr Emmett and another man, John Williams.
Doughton then dropped the knife down a drain before he was stopped by police; he gave officers a false name, denied knowledge of the attack and spat in the face of a policewoman.
Mr Emmett, who was expecting his third child, died four weeks later after having to undergo a liver transplant in London. Mr Williams survived but suffered a serious stab wound to his back.
Judge Mrs Justice Nicola Davies said an aggravating feature of the offence was that Mr Emmett had been profoundly distressed while clinging to life at a specialist hospital unit in London.
As well as leaving behind twin boys, Mrs Justice Davies said Mr Emmett's daughter Lola would never get to know her father, known by the family as "Michaelee", because of Doughton.
After detaining the teenager, the judge also lifted reporting restrictions previously banning the press from revealing his identity.
She told the teenager: "Nothing they said or did could justify your taking of a knife - still less pursuing them down the road and in turn stabbing each of them.
"In taking the life of Michael Emmett you have robbed twin boys aged eight of their father. Lola, his daughter, born when her father was critically ill in King's College Hospital, London, will never know him."
The judge said Doughton had shown little remorse.
The court heard he had a low IQ and had behavioural difficulties from the age of 11.
He was also described as having a "severe conduct disorder" which had been caused by "genetic factors not associated with poor parenting".
A teenager who murdered a father-of-three has been told he will spend at least 15 years behind bars.