HONG KONG— A mainland Chinese mother who asked her son to relieve himself in a bottle in a crowded Hong Kong restaurant has sparked an outpouring of online anger in the latest bitter exchange over etiquette.

Manners have long been a source of tension in the southern Chinese city, with Hong Kongers routinely complaining about what they see as the unrefined social habits of their “nouveau-riche” mainland counterparts.

The Standard newspaper said the latest incident occurred over the Lunar New Year holiday—a time when mainland tourists flock in large numbers to the former British colony, popular for its shopping.

The mother, who had been enjoying a meal with her family, allowed her son to answer nature’s call in a bottle she normally carries for such purposes.

“But a female waitress saw us and spoke loudly, saying there is a toilet upstairs,” she wrote in an online forum later. “She repeated it five times until everyone was staring at me.

“My family and I were so depressed thanks to Hong Kongers’ discriminating against mainlanders.”

But her complaints met with little sympathy in Hong Kong, where locals have expressed a growing unease about their relationship with the mainland and its increasing financial and political clout.

The popular HKGolden online forum had hundreds of posts on the issue, with user “Black Flashlight” remarking: “Only dogs will pee everywhere.”

FallOutBoy, joked that “each table should have a toilet”, while others said the woman should stay away from Hong Kong.

A video of a mainland Chinese girl flouting rules against eating on Hong Kong trains last year drew similarly angry reactions, with mainlanders branded as “locusts” by locals and a Chinese professor calling Hong Kongers “the dogs of British colonialists”.

The criticisms may be having an effect. Hong Kong’s Post magazine reported over the weekend that a school of etiquette is about to open in Beijing, modelled along the lines of Swiss finishing schools.

Founded by Hong Kong businesswoman Sara Jane Ho, the “Institute Sarita” will offer “exclusive clientele lessons in being classy”, according to the magazine.

Hong Kong, a former British colony, maintains a semi-autonomous status since it returned to Chinese rule in 1997, with its own financial and legal system.

Hong Kongers also complain that the influx of mainlanders has strained resources and pushed up prices from baby formula to property.