Claiming to be the headman of a gang, he called the police emergency hotline 24 times over five days, hurling vulgarities and abuse at the officers.
Ng Chong Guan, 30, dared them to catch him and threatened to shoot them with a gun.
Later, he also intimidated a cabby over the phone, threatened a coffee shop worker with a penknife and assaulted a stranger after his girlfriend claimed the woman's baby stroller hit her.
Last Wednesday, Ng was jailed for 15 months and given an enhanced two-day jail term as he committed some offences while out of prison on a remission order.
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He pleaded guilty to 10 charges, including abusing public servants, voluntarily causing hurt, criminal intimidation, theft and mischief.
Another 22 charges were also taken into consideration.
His lawyer, Mr Henry Lim Ghim Siew, said Ng has antisocial personality disorder and a low IQ, and will be seeking treatment at the Institute of Mental Health.
Previously jailed for threatening to bomb a clinic in 2015 and the home of a woman who refused to be his girlfriend in 2016, Ng has a litany of past offences.
He was near the end of a remission order when he made the first call on Sept 23 last year.
At about 9.50am, Ng dialled 999, uttered a vulgarity and told the operator he was a "gangster headman", a "loan shark syndicate" and asked him to "come Geylang see me".
The operator dispatched police resources to Geylang but could not locate Ng.
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He was nabbed on Sept 27 after he again made a foul-mouthed call to the police, who were able to trace and arrest him that day.
Ng admitted that he made the call, claiming he was stressed.
In his submissions, Deputy Public Prosecutor Eric Hu said Ng was clearly recalcitrant. He wrote: "Deterrence must also feature as the dominant sentencing principle to guard against abuse of an emergency hotline."
Ng had also attacked a 37-year-old woman on Nov 28 last year in Sembawang.
The woman was pushing her baby in a stroller, going past him and his girlfriend, who were standing in the middle of the pathway at the void deck of Block 504B in Montreal Drive.
When his girlfriend claimed the stroller hit her leg, Ng got angry and chased after the woman, pushing, slapping and kicking her multiple times. He also pulled the victim's hair and slammed her head against the wall.
For threatening, abusing or insulting a public servant, he could have been fined up to $5,000 and/or jailed for up to a year.
For voluntarily causing hurt, he could have been jailed for two years and/or fined $5,000.
This article was first published in The New Paper. Permission required for reproduction.