He threw the first punch even when the incident did not directly involve him.
When Wong Zhen Kang's friend had accidentally bumped into another person at a club, Wong reacted – with a knuckle duster.
He grabbed his weapon and punched Mr Quek Zhi Whui first on his right temple, and next on his jaw.
Yesterday, Wong, 24, was sentenced to a total of nine months' jail for voluntarily causing hurt by means of a weapon and possessing an offensive weapon.
The incident had occurred at Club Trace on Magazine Road on Oct 17 last year.
Just before 1.30am, Wong and his friend Kenrick, were entering the club when Kenrick accidentally bumped into the victim, Mr Quek, then 36, who was leaving with a friend for a smoke.
Mr Quek gestured to Kenrick to step outside.
Deputy Public Prosecutor (DPP) Eunice Lau said it was a premeditated attack as Wong did not throw a bare punch but had armed himself with a knuckle duster.
DPP Lau said: "The accused (Wong) was not even involved in this initial misunderstanding, yet he intervened."
During mitigation, defence lawyer S.S. Dhillon said the incident was totally out of line with Wong's character.
Wong, whose parents were in court yesterday, had acted instinctively, Mr Dhillon said.
Mr Dhillon had earlier said the scuffle was brief - lasting about half a minute - and that Mr Quek had not suffered serious injuries.
But the court heard the 6cm by 5.5cm knuckle duster, attached to Wong's bunch of keys, had two sharp and protruding edges.
And the attack left Mr Quek bleeding from wounds on his face.
A medical report dated Nov 4 last year showed Mr Quek had two puncture wounds near his right temple, two scratch wounds on his right jaw, multiple scratches on both arms and a bruise on his left eye.