A man with Asperger’s Syndrome was killed with a single punch after using a racist term.
Andrew Young, 40, died after 20-year-old Lewis Gill lashed out in November last year.
The defendant, who was arrested in Croydon and admitted manslaughter at Winchester Crown Court last month, struck Mr Young after the victim exchanged words with an acquaintance.
Victor Ibitoye had been riding a pedal cycle along Charminster Road in Bournemouth on November 6 last year when he was confronted by Mr Young, who said it was a "dangerous" activity.
Mr Ibitoye was walking next to Gill's ex-girlfriend, Wendy Cagua-Rodriguez, while the defendant walked behind.
He threw a single punch, connecting with Mr Young's temple, after hearing the victim say to Mr Ibitoye: "Why don't you go back to the jungle?"
Kerry Maylin, prosecuting, showed CCTV footage of the incident to Salisbury Crown Court yesterday afternoon before the defendant was sentenced.
She said: “The defendant claims he was worried about Andrew Young because he thought he was being menacing.
"He said Andrew Young put his hand to his pocket and he thought he was going to pull out a knife or a gun."
However Judge Keith Cutler said Mr Young did not represent a threat, and sentenced him to four years in prison for manslaughter.
He was also sentenced to two three-month prison terms to run consecutively for committing the offence while on a suspended sentence for robbery, and for handling stolen goods.
Judge Cutler said: "You are a powerfully built young man.
"You must have known that it was going to cause a significant injury, and very sadly, it did."
Mr Young died the following day, November 7, following surgery at Southampton General Hospital.
He struck his head on the pavement after the punch, and a postmortem found no injuries to suggest that he had tried to defend himself.
The former Bournemouth School pupil, who spoke a number of languages, was a member of St Edmund Campion Church in Bournemouth.
He used to work for Asda at Castlepoint shopping centre after leaving university, and was once a member of the naval section of the Combined Cadet Force.
Mum Pamela, who sat beside her son when he died, said: "Andrew had the social skills age of a 14 year old.
"He was very precise and particular because of his Asperger's and he wouldn't have liked seeing someone riding a bicycle on the pavement because it was dangerous.
"I sat with him when he died. I wish that awful man [Gill] who took my son away had pleaded not guilty so he would have got longer."
Detective Inspector Marcus Hester, of Dorset Police’s Major Crime Team, said: “This was a violent attack on an innocent man which had a tragic outcome.
“This case shows that violence does not resolve anything and can have far reaching consequences not imagined at the time.
“Today the court has issued a sentence deemed appropriate and in accordance with the evidence put to them.
“Criminal behaviour such as this will not be tolerated and we are committed to bringing offenders to justice.”
The Crown Prosecution Service prosecutor in the case was Kerry Maylin.