He tried to be a Good Samaritan and asked a fellow train passenger to give up his seat to an elderly woman.
But the situation quickly turned ugly when odd job labourer Chin Poh Heng thought that Mr Chen Zongxi, 32, was slow in getting up from the reserved seat.
Chin, now 49, became agitated and punched the Chinese national several times before kicking him.
He was jailed for two weeks yesterday after pleading guilty to one count of voluntarily causing hurt to Mr Chen.
An unrelated criminal intimidation charge was taken into consideration.
According to court documents, Chin had threatened to throw a chair at a woman in a Sembawang Vista flat on Sept 24, 2014.
In the MRT incident, which occurred on Sept 2 last year, the two men were on the train heading towards Newton station when, at about 11.45pm, an elderly woman entered their cabin.
Chin tapped Mr Chen's shoulder and asked him to give her his reserved seat.
Deputy Public Prosecutor (DPP) Ryan David Lim said: "Prior to the train ride, the victim had consumed a few cans of beer, and thus informed the accused that he needed some time to stand up.
"The accused perceived that the victim was being slow in giving up his seat to the elderly lady."
Chin became agitated and punched the left side of his victim's forehead several times with his right hand.
Mr Chen covered his head to shield himself from the punches.
But Chin continued attacking the construction worker and kicked him once at his stomach.
Chin tried to get off the train when it stopped at Newton station, but other passengers stopped him.
Mr Chen then pressed an emergency button in the train to alert SMRT staff, who arrived soon after to detain the pair.
Mr Chen was taken to Tan Tock Seng Hospital. A medical report stated that he suffered bruises around his eyes and left forehead, and a cut over the bridge of his nose.
He was given two days of outpatient medical leave.
For voluntarily causing hurt, Chin could have been jailed up to two years and fined up to $5,000.
This article was first published on May 19, 2016. Get The New Paper for more stories.