Tokyo - Crowd-surfing, human pyramids and rugby practice - boisterous behaviour by fans on Japanese trains has stirred some criticism as the uber-polite country hosts the Rugby World Cup.
Two weeks into the tournament, rugby fever has started to catch on in Japan, and many teams and their supporters have been bowled over by the warm reception they have received.
But a handful of rambunctious supporters have found themselves the subject of online debate and some critical media coverage after violating Japan's famously reserved social norms.
Among them are a group of six Australia supporters, decked out in Wallabies t-shirts, who decided to form a human pyramid on a train in Sapporo in northern Japan.
"I got on the Toho line and it wasn't Japan," a Japanese Twitter user said, posting a video of the antics, which has been viewed over 226,000 times and attracted disgruntled comment.
"This is annoying. They think they can do whatever they want because they're travelling but it's an insult to the country they're visiting," one user replied.
Loud disturbances are relatively rare on Japanese public transport, where people avoid taking or making phone calls, keep their music quiet, and carry on conversations discreetly.
There are exceptions, including late-night trains where drunken salarymen can sometimes be seen yelling at passengers or each other.
But even the morning commuter crush, when millions find themselves squished together on packed trains, sometimes throwing elbows to grab a spot, tends to be conducted silently, albeit through gritted teeth.
The human pyramid is not the only instance attracting attention, with other viral videos showing French fans seated on a carriage floor passing a crowd-surfing friend overhead, or supporters singing loudly.
And one widely viewed video shows a group of fans, some in Scotland and England shirts, playing rugby on a train, passing around a yellow ball and mock-tackling each other.
"Don't do this. You're in Japan," one commenter wrote.
"You should visit a foreign country only after studying about it," added another.
But others have brushed off the incidents, with one saying the mock rugby match "looks fun".
Domestic media have picked up on the controversy, with one even airing a segment entitled: "Trains are dangerous with rugby fans!"
Japanese officials stress that rules in place against disturbing other passengers are intended to keep everyone safe and comfortable.
"We hope that many foreigners take part in the sporting festivities during the Rugby World Cup this year and the Olympics next year, but for us the most important thing is to ensure their safety," Mineo Matsui, director for community safety at the Tokyo Metropolitan Government, told AFP.
"We understand that they are excited and they want to show it, but they need to know how to control themselves."
By and large, any criticism has been vastly outweighed by positive coverage and sentiment towards the tournament, the hosts and the visiting teams and fans.
Venues have been packed out, even for fixtures with bottom-ranked teams, and Japan's shock victory over Ireland has sent excitement soaring.
Meanwhile, foreign teams have won plaudits for adopting Japanese customs, including bowing to fans after games and tidying their changing rooms.