He checked into Hotel 101 at Geylang Lorong 12 at about 1am on Thursday.
Nothing unusual - until he barricaded himself in the room on the eighth floor 12 hours later.
The Caucasian man, believed to be in his 50s, used the furniture in the room to block the door.
He then flung the toilet cistern cover out of the window.
The lid, which weighed about 4kg, hit a car belonging to a bystander who wanted to be known only as Mr Wong.
The 49-year-old had parked his car below the hotel before going to a nearby coffee shop for a drink.
He said: "I was at the coffee shop when someone said he heard that rocks were thrown out of a hotel room and my first reaction was to rush back to check on my car. I was sure my car was done for."
His car was badly scratched as a result.
Alarmed hotel employees called the police at about 1.20pm.
The Singapore Civil Defence Force (SCDF) sent a Red Rhino, two fire bikes, an ambulance, two support vehicles and a fire engine to the scene.
An air bag was set up at the foot of the hotel and the area was cordoned off by police, attracting crowds of onlookers.
Renovation worker Huang Meng Ho was unaware of what had happened until he saw the police cars.
"There were many police cars and SCDF vehicles outside the hotel, and I thought it was a hostage situation," said the 28-year-old.
"Before that, there was the sound of windows shattering but there wasn't any shouting or noise afterwards," he added.
The Caucasian man was arrested after a three-hour stand-off with police.
Wearing sunglasses and a white top, he was seen smiling at the cameras while in a police car.
He was arrested under the Mental Health Act.
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