The three-year-old monkey is called Godzilla, and hangs out at a market stall in the Min Buri district of Bangkok, with visitors seen crowding around trying to feed him earlier this month.
Godzilla was wearing a tight-fitting t-shirt while tied to the stall, with a video showing him biting on a water bottle and pushing away people's hands as they tried to pet him.
While macaques normally weigh between eight and 10 kilos, Godzilla is already double the average weight for his species - now weighing more than 20 kilos.
Shopkeeper Manop said she had adopted Godzilla when he was abandoned by a previous owner, and that she feeds him and treats him well.
However, she said she's been unable to get his weight under control, explaining: "The rescue team found Godzilla when he was very small.
"And since he grew up being fed by humans, he does not know how to find food on his own in the wild."
Manop said Godzilla exercises every morning, but still remains obese.
She also said he does not like being touched by strangers, and will start to behave wildly if he's not keen on someone.
Manop continued: "I bring Godzilla with me to the market where I can look after him. I don't like him to be on his own because he gets stressed.
"A lot of people give Godzilla food but he only eats from people he likes. He's very fussy and can get angry if he doesn't like the person."
The animal's plight is similar to that of a wild monkey known as Uncle Fatty, whose weight ballooned after gorging on junk food from passersby in Thailand back in 2017.
Along with his huge belly, another nasty side-effect of his diet was that he no longer needed to forage, so he didn't perform as much exercise as the other monkeys.
He was later sent to 'fat camp', but was last seen in June 2019 before going missing - and is now presumed dead.
Godzilla is almost as heavy as Uncle Fatty, who tipped the scales at 27kg, and was believed to be between 10 and 15 years old.Featured Image Credit: Viral Press