The defendant pulled over and approached the man in a "menacing manner", claiming to be a member of the Mongrel Mob, the court heard.
While the victim asked Dolan to back off, the teen's anger only swelled.
He threw a "haymaker", which caused a large welt to the left side of the victim's face and knocked his cellphone from his hand, damaging it.
Dolan continued ranting and yelled that he would get his gang-member friends to continue the violence.
He shouted at the victim and others in the vicinity that he had "just attacked n...".
There were several members of the public who witnessed the assault and racist slurs; police were called and Dolan was arrested at the scene.
Aside from the motive for the attack and its unprovoked nature, Judge Rollo said there was a further concerning aspect.
In March, Dolan had been sentenced to community work and supervision for an assault on a teenage family member.
He was in the middle of completing that sentence when the Moray Pl incident occurred.
Despite the seriousness of the incident, the judge was impressed by a letter Dolan wrote apologising for his actions.
"You say that you're disappointed in what you've done and will take all appropriate steps to avoid behaving in this way in future," he said.
Dolan was sentenced to 120 hours' community work (to be added to previous sentence) and $900 reparation.
