Uriah Gardner, 16, plunged a knife into the chest of 17-year-old Fico Dougan with such force that it emerged from his back.
Gardner launched the unprovoked attack at a house in Croydon, south London, in the presence of a two-year-old girl.
The teenage killer had been listening to rap music in the hours before the attack, and admitted the violent lyrics made him want to ‘stab up someone’s face’.
Without warning, Gardner grabbed a kitchen knife and stabbed Fico as he sat on the sofa watching TV.
He dumped the knife in a drain and fled the scene on a bus before trying to burn his jeans in his back garden.
Psychiatrist Dr Philip Joseph, who has examined some of Britain’s most dangerous killers, described Gardner as a ‘budding psychopath with a potential for violence’ during his trial.
Gardner was today sentenced at the Old Bailey and ordered to serve at least 14 years in custody before being considered for release.
The court heard he has a previous conviction for sexually assaulting a girl when aged just 12, and has a string of convictions for robbery, theft, assault, and criminal damage.
Judge Stephen Kramer said: ‘You deliberately picked up the knife, you went to the lounge with it and deliberately used it in anger to kill Fico.
‘It was a senseless killing of someone you had only met and been with for a few minutes.
‘You have deprived a family of a much loved son, grandson, and brother.’
The judge said an independent psychiatric assessment had found Gardner was not mentally ill, but had some of the traits of an emerging personality disorder.
‘The initial shock of it all has now given way to the reality that Fico has been killed by someone he did not offend and had no chance to defend himself.
‘We are living with numbed emotions because we are struggling to be strong for each other and suppress the pain and sense of injustice.
‘Fico was very unique in his own way.’
Fico died from a stab wound to the heart soon after the attack on September 25 last year.
On the day of the attack Gardner visited his 19-year-old sister and her friend Montana Riley at a house in Ockley Road, Croydon.
He was listening to music on his headphones and said: ‘When I listen to rap music I want to stab somebody’.
Fico, who was going out with Miss Riley, arrived at the house and was watching TV with them.
The killer suddenly left the room with a ‘vague stare’ on his face and went into the kitchen.
Shortly afterwards he burst into the living room holding a large kitchen knife and without warning attacked Fico who was sat on the sofa.
Fico’s girlfriend desperately tried to stop the stabbing as Gardner attempted to lash out another five or six times with the knife.
She was screaming for him to stop but he paid no attention.
Miss Riley said: ‘He came out of nowhere and leapt over his sister to get to Fico.
‘He was just stabbing Fico constantly. I tried to get between them and stop him.
‘He looked like he was trying to stab his face so I had my hands over his face and his heart.
‘I was trying to talk to Fico and to see if he was breathing but he wasn’t responding. His eyes had rolled back.’
Miss Riley told detectives the teenager had been listening to music on his mobile phone in the hours before the attack.
She told them: ‘He said, “When I listen to depressing songs I feel depressed, when I listen to love songs I feel sexually frustrated, and when I listen to rap music I want to stab up someone’s face”.
‘He started clenching his fist. I thought it was weird but you don’t think he actually would. He did not look serious.’
Fico, who had been studying for a BTEC in Business Management at John Ruskin College, suffered a 14cm deep wound to the chest which passed all the way through his body, penetrating his heart.
He also suffered a stab wound to his left armpit and a cut on his left arm and was pronounced dead at hospital at 3.15pm.
Gardner fled the house after the attack and dropped the knife down a drain before getting a bus home.
Neighbours spotted him trying to burn clothing in the back garden and he told them it was ‘stuff that was not good enough to take to the charity shop’.
Gardner denied murder, but was convicted after a one-week