Alexandra Harcharek will never forget the first time she was anointed the “mayor” of the Benjamin Franklin Bridge in Philadelphia. It was an overcast Wednesday in April and she was driving to the city on her last day of an internship.

Never mind that she had to drive 15 minutes out of her way from her apartment in Sewell, N.J., to her desk at the Philadelphia City Paper. Or that it involved having to pull out her iPhone while weaving through morning rush-hour traffic to “check in” to the Foursquare application.

Once she tasted “mayorship,” she was hooked. “Being the mayor of a major bridge — how cool is that?” said Ms. Harcharek, 21, who currently runs a food blog, afoodcoma.com. She was so excited by her “nerdy achievement” that she posted a Twitter message about it.

Then, 17 minutes later, she was out of office.

While Foursquare has been talked about in corporate boardrooms as the next big thing in social media — it has some 2.5 million users — it has also spawned a more trivial pursuit: a petty and vicious battle over virtual pieces of turf.

Strangers are locked in bitter rivalries. Workplaces have been carved up into virtual battlefields. College campuses have become factionalized. Even some homes have become social media minefields.

Not bad for a feature that was never part of the original concept for Foursquare. Dennis Crowley, a founder, said the idea for becoming a mayor was born from a passing joke made by Chad Stoller, a friend and adviser, about the huge amount of time that Mr. Crowley and his partner, Naveen Selvaduri, were spending in a Greenwich Village cafe, hashing out their Web idea. “You two should be mayor,” Mr. Crowley recalled Mr. Stoller saying, in reference to the cafe. (Foursquare shuns the stuffy “mayoralty.”)

But like many fads in the age of Twitter trends and viral videos, it has taken on a life of its own. Even more baffling is why users have become so emotionally invested in being a mayor, as there are few, if any, tangible benefits. While some bars award free beer and some shops give small discounts as a marketing ploy, the majority do not.

Full story: Who Elected Me Mayor on Foursquare? I Did – NYTimes.com