Siroosh Bavarsad, 31, was annoyed when he heard Graeme Noble complaining about his establishment, the Clock Tower, on the day it opened.
Mr Noble had complained about table napkins and not getting a roll with his soup. When Bavarsad heard raised voices he raced through from the kitchen area and headbutted Mr Noble, knocking him unconscious.
Bavarsad, from Glasgow, pled guilty at the city’s Sheriff Court to assaulting Mr Noble on 6 March last year.
Passing a sentence of a community payback order with 150 hours of unpaid work, Sheriff Martin Jones QC branded Bavarsad’s behaviour “disgraceful”. He also ordered him to pay Mr Noble £1,500 compensation.
Procurator-fiscal depute Pauline Henderson said: “The accused is described to have flown into a rage and headbutted the complainer once to the face, which knocked him to the floor.
“Medical staff having lunch in the restaurant tended to the complainer and summoned both ambulance and police.”