The practice of men sitting in public transport with their legs wide apart, taking up more than one seat, has long been an irritant and the term "manspreading" appeared in 2014 in New York following a campaign against it there.
In Madrid, buses have since Thursday been kitted out with stickers banning the habit, which appears next to signs telling passengers to use their phones in moderation and keep things tidy.
"Respect other people's space," it reads.
The stickers are due to be rolled out in 2,000 buses belonging to Madrid's Municipal Transport Company.
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Melisa Garcia, a 30-year-old from Madrid, thinks it's a good idea.
"It's a total lack of respect and education," she says, adding the last time her neighbour manspread on the seat next to her, she "kicked him".
"I told him: 'the seat you have is big enough for you'."
The sticker comes as the campaign #MadridSinManspreading ("Madrid Without Manspreading") rages on Twitter, launched by the "Women Fighting" feminist collective.
It adds that men, on the other hand, "have been given a sense of hierarchy and territoriality, as if the space belonged to them."
Robert Durou, a 75-year-old retiree, backed the campaign.
"Before... People were more respectful of others," he lamented.
David Correa Clares, meanwhile, admitted he has been guilty of manspreading in the past.
That's what the conservatives who lead the Madrid region -- and manage the subway -- think, estimating that the rules of "one seat per person" are clear enough.