“Robin Hood Airport is closed,” Mr. Chambers, then 26 and a financial supervisor, said to his 690 followers, who included the woman, known on Twitter as @crazycolours. “You’ve got a week to get your [expletive] together, otherwise I’m blowing the airport sky high!!”  That would have been the end of it. But Mr. Chambers’s impulsive outburst led him down a long and unexpected path, turning him into both a convicted criminal and a cause célèbre for Twitter users and free-speech advocates in Britain and beyond.  On Thursday, after a judge in this South Yorkshire town refused to overturn Mr. Chambers’s previous conviction for causing a “menace,” ordered him to pay about $4,800 in costs and fines, and icily lectured the courtroom about the impropriety of sending Twitter updates during the case, Mr. Chambers’s outraged supporters let loose.  The actor and Twitter enthusiast Stephen Fry offered to pay his court bills. Other users began raising money for a new appeal. And on a new and wildly popular trending topic, #IAmSpartacus, people began defiantly expressing their solidarity with Mr. Chambers by reposting his offending Twitter message or by threatening to blow up other, random, things. These included Downing Street, the courtroom, the town of Doncaster, Gatwick Airport, Robin Hood the person, the White House, the Basingstoke Hockey Club, “everyone,” “my garage,” some balloons, and NBC (if it canceled “The Event”).  “I think I’ll blow up Parliament,” one person wrote. “Oh, wait, that was a JOKE.”  That none of these people appear yet to have been arrested for doing the exact same thing that Mr. Chambers did shows how hard it has become for law enforcement officials to know how to respond to the anarchic culture of social media sites, especially Twitter, with its rapid-fire, off-the-cuff, often satirical exchanges.  “Whenever you get a new media coming in, the law is always slow to adjust,” said Rupert Grey, a media lawyer at Swan Turton in London. “In some respects, the reaction of the tweeters is irresponsible, but the authorities have to understand that this is the world we live in and people are going to say these things.”  While the judge who rejected Mr. Chambers’s appeal, Judge Jacqueline Davies, declared that “any ordinary person” would be alarmed by Mr. Chambers’s message, free-speech advocates said that they were not alarmed at all and that her conclusion represented the failure of traditional law to grasp the changing conventions of new media.  “The authorities don’t seem to understand the way Twitter works,” said Padraig Reidy, news editor of Index on Censorship, a London magazine that covers free-speech issues. “There’s no provision in the law for people being hyperbolic, sarcastic or ironic. For a country that prides itself on its sense of irony, that is unfortunate.”  It was a fluke, really, that brought Mr. Chambers’s stray Twitter message to the attention of the authorities. An airport manager doing a search on Twitter for Robin Hood Airport-related items on his home computer saw the message a few days later and reported it. A few days after that, five police officers arrested Mr. Chambers at work, interrogated him for eight hours and seized his computers and phones.  “Do you have any weapons in your car?” they asked, Mr. Chambers told The Guardian this fall.  “I said I had some golf clubs in the boot,” or trunk, he responded, “but they didn’t think it was funny.”  He was convicted of sending a “menacing message” over a public telecommunications network under the Communications Act of 2003.  He was fired from his job as an administrative and financial supervisor at a car-parts company. He moved to Northern Ireland to live with @crazycolours and was fired from a subsequent job after his employers discovered his criminal record. He is now unemployed. Judge Davies said she found him an “unimpressive” witness.  “Anyone in this country in the present climate of terrorist threats, especially at airports, could not be unaware of the possible consequences” of his Twitter message, she said.  It is unclear how people on Twitter would have responded had Mr. Chambers been, say, a Muslim living near Manchester. Though many users seem consistently to argue for the unfettered right to say anything on the site, reaction has been less uniform in a second case. On Thursday, a local official in Birmingham was questioned by the police after responding to the comments of a newspaper columnist who is a Muslim woman by posting on Twitter: “Can someone please stone Yasmin Alibhai-Brown to death?” (He quickly apologized and removed the message; he has not been charged with a crime.)  But Mr. Chambers is an ideal Twitter hero, so immersed in life on the site that, he said, he sent 14,000 tweets in the 11 months before his offending message.  In testimony on Thursday, he tried to explain that speaking on Twitter is often like bantering facetiously with friends.  “People who know me and work with me make these comments all the time — ‘I’m going to kill you if you don’t get me a coffee in a minute,’ ” he said. Of his message, he said: “To me, it was clear that it was hyperbole.”  The high-profile case lured a band of angry tweeters and bloggers to the courtroom on Thursday, where they spent breaks tweeting, blogging and railing about what they saw as the erosion of civil liberties in Britain.  “It could be any one of us,” Steve Page, 39, a graduate student in neuroscience at the University of Hull, said in the hallway outside the courtroom. “Every single person I know has said something on the Internet that could be classified as criminal if someone took it like that.”  Mr. Chambers said he did not know whether he would seek to appeal further.  But the pro-Chambers momentum was snowballing on Twitter, where #IAmSpartacus — a homage to the Kirk Douglas movie in which rebel slaves in ancient Rome refuse to betray their leader, Spartacus, confusing the enemy by claiming that they are all Spartacus — was the top trending topic on the site Friday.  “I am Paul Chambers!” one person posted on Twitter.  “I am going to blow up the entire universe with my giant spaghetti bomb,” another said.  Someone else asked, referring to the abbreviation for “laughing out loud,” “If I put ‘lol’ at the end of every tweet, will that protect me from prosecution?”
Paul J. Chambersâs joke on Twitter about blowing up an airport got him convicted, but he is now a cause cÃ©lÃ¨bre.