The Bill of Rights do not convey absolute rights according to the Supreme Court, but provide a balance between the public, the individual and the government. The 1st amendment in particular is balanced between the public's right to free flow speech vs. the individuals right to privacy and truth.
There are no federal defamation laws, but many states do have such laws which do not impose criminal penalties but allow individuals to sue for civil liability. The best explanation for this question would be found in the Supreme Court case Sulllivan v. NYtimes which discusses the public's right to the free flow of speech vs. the individuals right for protection against defamation. Generally, actual malice, i.e., intent to do harm, is necessary in order for there to be criminal defamation. While this case applied the actual malice standard to public (or prominent) individuals, private individuals do not have to show actual malice but must prove actual damages (punitive damages require a showing of actual malice) see Gertz v. Robert Welch. The individual must show that the statements are false and that they were actually damaged in some fashion and that money will remedy that damage.
The most recent decision involving defamation is the Stolen Valor Act which the Supreme Court struck down this year, holding that the government did not have a compelling interest in prosecuting those who lie about their military service.
"Remember to always be yourself. Unless you can be batman. Then always be batman." Unknown
