Reginald Tutu thrust the knife into the neck of the unsuspecting victim after developing “paranoid suspicions” about him as he sat waiting for a haircut.
A court heard Tutu, 22, left the premises on Harehills Road, Leeds, and returned with a knife before attacking his victim.
Leeds Crown Court was shown CCTV footage of the victim being attacked as he stood in the doorway of the shop, called Hakuna Matata, looking at his mobile phone.
Tutu, of Throstle Terrace, Middleton, had been smoking ‘spice’ - a manufactured cannabis substitute - shortly before the attack, which took place on November 17 last year.
Jonathan Sharp, prosecuting, said: “He said some words that (the victim) did not understand and then said ‘I’m going to kill you’. He produced the knife and stabbed him once to the neck.”
Tutu then got back into his car and drove off. Mr Sharp said: “(The victim) was in immediate pain and ran back into the shop shouting.”
The victim was taken to hospital and underwent surgery. The knife had narrowly missed an artery in his neck.
In a statement made after the attack, he described how he now feels “fear, panic and even phobia” when he goes out in public.
He added: “I still can’t sleep at night and this has caused me a disability which I will have for the rest of my life as it impacts the movement of my mouth when I am eating, laughing or even when I turn left.”
Tutu was arrested after he contacted his solicitor later the same day and said he thought he may be wanted in relation to a stabbing.
He pleaded guilty to wounding with intent and possession of an offensive weapon.
Tutu has a previous conviction for robbery and at the time of the attack was subject to a suspended prison sentence for burglary in which a 13-year-old boy was threatened.
The court heard Tutu has a history of mental disorder, made worse by his refusal to accept treatment and his heavy daily use of cannabis and similar drugs.
A psychiatrist, who assessed Tutu as dangerous, said he may have carried out the attack for no reason at all other than seeing the victim may have generated “fleeting paranoid suspicions”.
Matthew Harding, mitigating, said Tutu was still unable to provide a clear explanation of his motive for the attack.
He added: “He maintains that he was unwell at the time and he also had his underlying mental health difficulties.”
Judge Tom Bayliss, QC, handed Tutu a life sentence, telling him he continued to pose a serious risk to members of the public.
He must serve a minimum of four years in prison before he is eligible to apply to the parole board for release but the judge warned Tutu he may be in custody for many years.
The judge said: “You are an extremely dangerous individual who will be prone to acts of unpredictable violence in the future.
“The victim was an innocent, unsuspecting member of the public, a complete stranger to you, a man simply going about his everyday life and for no reason at all he was attacked by you.”