When Ng Hwa Lee heard his uncle had been harassed by a loan shark, he leapt into action.
He rushed to his relative's block, noticed a man with tattoos getting out of a lift - and attacked him with a knife.
The "loan shark" turned out to be an innocent 22-year-old who was about to take his girlfriend home on his motorcycle.
On Tuesday, the overzealous sales engineer was jailed for seven months.
The court heard it was the victim's tattoos that led to the case of mistaken identity.
After hearing about his uncle being harassed, Ng raced to the block in Woodlands Drive 52.
There, the 34-year-old father of one - who had been drinking - took one look at the ink on Mr Sim Beng Hui's legs and assumed he was the loan shark.
He asked the technician what he was looking at in Chinese. The victim replied that he was not looking at him.
Deputy Public Prosecutor Claire Poh said Ng then blocked Mr Sim's path and punched him in the face. In a bid to defend himself, Mr Sim swung his right hand, in which he was carrying two motorcycle helmets, at his attacker.