Have you ever experienced the annoying moment of completely losing your appetite over smelling Chinese pancakes or steamed stuffed buns held by nearby passengers aboard a confined subway car? Then how would you feel at sight of people enjoying an actual full course meal on a crowded subway as if they were in a dining room?

A group of unnamed foreign passengers apologized after doing just that. The group recently threw a "dinner party" several days ago on the Shanghai subway, which was swiftly followed by a disciplinary conversation with local police. The quartet also “realized the negative impact they brought on public transportation,” according to an announcement posted Wednesday on the official Weibo account of Shanghai Metro.

The apology came after a photo captured the group wining and dining in the middle of a carriage on Metro Line 11, complete with a foldable table and various foods. The photo was posted by a Weibo user on Friday, and stirred up widespread indignation online.

While many netizens have condemned the foreigners' unscrupulous demeanor, others have questioned the supposed double standard as to why foreigners were allowed to eat onboard while Chinese locals were not.

Shanghai Metro authorities responded to the incident Monday amid the ever-growing concerns by saying that the group had obviously breached the city’s rules and regulations for riding the subway, which specified that passengers should not “eat or talk loudly” while on the train.

But a subway official later confirmed to Shanghai’s Eastday.com that no punishments would be actually meted out to the diners, since the rules and regulations are not legally binding and there are no specific laws charting out the penalties for rule breakers.

Recognizing their improper behavior, the quartet wrote a letter of apology on Wednesday after talking with local police as well as officials from the city’s subway authorities. In its latest Weibo post, the Shanghai subway introduced new development of the case and also called on passengers to make joint efforts in safeguarding the security as well as the sound environment of the city’s underground transportation.

It is in fact not the first time that the lack of boarding courtesy has triggered massive public outcry.

Last January, a woman was spotted on Shanghai’s Metro Line 1 devouring chicken feet and spitting the remains all over the carriage, despite passengers’ outrage. A bunch of livestreaming hosts last May were also seen filming themselves eating and hanging up clothes on the subway in the southern city of Guangzhou, evoking huge online backlash, with many expressing their wrath.