The 17-year-old Bedfordshire resident became upset after watching a TV documentary about 9/11, leading him to compose an expletive-laden e-mail that called U.S. President Barack Obama a "prick." The FBI took the e-mail very seriously and contacted the local British police, who visited Angel at his home and took his picture, then informed him that he would not be able to enter the U.S.
It has become necessary for government officials to monitor e-mail and other social media to find potential threats. Last year, the nation of Colombia arrested a man who used Facebook to announce, "I promise to kill Jeronimo Alberto Uribe, son of Alvaro Uribe." Alvaro Uribe was the president of Colombia.
While we harbor a healthy skepticism about some of the FBI's online monitoring ambitions, it's perfectly legit to use e-mails sent directly to the government to identify threats. That said, Angel claimed that he was drunk when he wrote the e-mail, so he might not be a long-term threat — but maybe you can never be too careful.