A footballer will not face charges over a homophobic tweet he posted about Olympic divers Tom Daley and Peter Waterfield.
Director of Public Prosecutions Keir Starmer said Daniel Thomas's message was "not so grossly offensive that criminal charges need to be brought" - and said the divers both agreed with the decision.
He added that new guidelines for prosecutors on social media cases would also be issued, given the growing number of complaints.
Daley, 18, and diving partner Pete Waterfield finished fourth in the 10m synchronised dive at this Summer's Olympics.
Thomas, a midfielder at Welsh Premier League side Port Talbot Town FC, posted a homophobic message on Twitter, which was quickly deleted but later distributed more widely - leading to his arrest.
Mr Starmer said: "This was, in essence, a one-off offensive Twitter message, intended for family and friends, which made its way into the public domain.
"It was not intended to reach Mr Daley or Mr Waterfield, it was not part of a campaign, it was not intended to incite others and Mr Thomas removed it reasonably swiftly and has expressed remorse.
"Before reaching a final decision in this case, Mr Daley and Mr Waterfield were consulted by the CPS and both indicated that they did not think this case needed a prosecution."
He said the message was intended to be humorous and that Thomas had not intended it to go beyond his followers, who were mainly friends and family.
Mr Starmer added: "the time has come for an informed debate about the boundaries of free speech in an age of social media".
He said new guidelines were needed because this was just one of a growing number of such cases and there were likely to be many more.
Estimates show there are 340 million messages a day sent on Twitter alone and "banter, jokes and offensive comment are commonplace and often spontaneous", he said.
"Communications intended for a few may reach millions."
Mr Starmer, the most senior prosecutor in England and Wales, will hold a series of round-table meetings with campaigners, media lawyers, academics, social media experts and law enforcement bodies next month before the interim guidelines are published.