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At the end of the first week of school the teenagers poured into the crowded suburban discotheque by the dozens, leaving their backpacks at the door. They rushed onto a dance floor covered in shoulder-high soap suds and started shaking their hips, some grinding against each other in the sexually suggestive dance that is the trademark of this city's newest youth craze.

Thousands of lower-income Mexico City teens have become obsessive imitators of a Puerto Rican subculture based on garish street fashions and the throbbing blend of reggae, hip-hop, and Latin music called "reggaeton." Nearly every weekend for more than a year, youths known as reggaetoneros have amassed by the hundreds in metro stations before heading off to dance at clubs or clandestine parties, taking over entire subway cars and singing their favorite songs as loudly as possible.

But Mexico City, a bastion of liberalism in a conservative country, is showing little tolerance for poor, raucous youth imitating a foreign subculture most have seen only on the Internet. Reggaetoneros are increasingly being met with open hostility and even violence.

Last month, hundreds clashed with police after a party was canceled in the downtown nightlife district called the Zona Rosa because more people showed up than could fit into the bar where it was being held.

Authorities said that as many as 600 angry youths who couldn't get into the club went on a rampage at local subway stations, damaging turnstiles and streetlamps. Police detained 200 of the young people. None were charged, and they were released within a day.

Two weeks later, reggaetoneros gathering at the Chabacano metro station were assaulted by a group of young men who had planned their attack on Facebook. Surveillance cameras caught more than a dozen young men kicking a prone reggaetonero and whipping him with their belts.

The Facebook page was one of at least a dozen launched in the last year that urges people to kill or beat up reggaetoneros. YouTube videos ridicule reggaeton music and the way its fans dress.

Many of the attackers are members of porros, descendants of informal student groups created by the government in the 1960s to quell student uprisings. Today, they have transformed themselves into youth gangs that operate out of high schools and universities, where authorities have limited powers to enter.

A member of one porro group, who asked not to be identified for fear of reprisal, said the groups have beaten up reggaetoneros on at least four or five occasions because "they feel superior and are acting like the metro stations belong to them."

Sociologists say, however, that reggaetoneros are being stigmatized because they come from rough neighborhoods and because of the way they dress.

Mexican reggaetoneros of both sexes tend to tweeze their eyebrows and wear skin-tight, neon-colored pants, loud jewelry, thick-framed eyeglasses and bedazzled baseball caps worn sideways. The boys wear their hair in cropped bowls or gelled mohawks. Girls dress in tight, spangled tops, their bangs gelled to their foreheads.

The sexually explicit lyrics of reggaeton and the music's iconic dance move known as "perreo," or dancing doggy style, has also made them a target.

A Facebook page that describes reggaeton as "grotesque, stupid noise that obstructs neurons" calls on people to "end with that horrible plague" and to kill reggaetoneros "for your country."

Jose Antonio Perez Islas, who coordinates the youth research seminar of Mexico's National Autonomous University, or UNAM, says the kids just want to have fun.

"These types of groups are the only outlet these youths have to socialize," said Perez. "Most don't go to school, and many work in the informal economy; their families are in total crisis and most have to socialize on the street and in groups."

While reggaeton has been popular in Mexico for at least seven years, reggaeton fans began forming clubs, or combos as they call them, on Facebook about two years ago, when the groups began showing up at subway stations they picked as a gathering point.

"They plan to meet in known places because most don't know the city and they accompany each other to get to the (party) venue because in a group the trip is safer," Perez said.

With clubs with names like "Class and Style," ''Gum Poppers," ''Hit Men," ''The Family," and "The Danoninos" — after the yogurt brand — the teenagers post photos of their outings, exchange music, gossip and news about upcoming dances.

Monserrat Gomez, 18, lives in a two-bedroom house with six other family members in a working-class neighborhood downtown. She dropped out of high school to help her ailing mother and now works three days a week at a quesadilla stand, earning $11 a week for her work.

Last year, a friend invited her to join the Liverpool combo and she did because it was free and reggaeton nightclubs often give a discount on the $2 to $4 cover charge when people arrive in a large group.

"For me, it's a way to clear my mind for a while, to have fun," said Gomez.

But for Christopher Rodriguez, a 17-year-old high school student, those clubs may be a thing of the past. He used to belong to a club that often met at a metro station about an hour's subway ride from the capital's downtown.

Because of the negative attention, many of the teenagers are now trying for a lower profile, preferring to travel in small groups to their dances. And Rodriguez has opted to forego the clubs altogether.

"Rivalries with other groups started and it became a big mess," he said, "So I decided to leave."