Hockley left the store and was followed by Mullen who punched him once to the face without warning, causing the victim to fall back and hit his head on the concrete wall.
Mullen then walked towards McDonald's on Camp St.
Judge Callaghan said the victim had some issues with concentration, spells of dizziness and tenderness to his jaw.
His victim impact statement said one of the people he was with welcomed a child a couple of days after the incident.
"He expresses the opinion he could easily have ... hit his head and never got to meet the child. He says this type of incident needs to stop.''
Mullen had no history of violence or convictions for assault since 1995 and while restorative justice may have been "the answer", Mullen declined to take part.
Judge Callaghan ordered him to pay the emotional harm reparation in full within 14 days.