Among other things, Golb has argued that his email impersonation of the NYU professor was parody protected by the First Amendment. As Hustler Magazine makes clear, acts of parody are entitled to broad constitutional protections. The more difficult issue presented by the Golb situation, however, is whether his impersonation can be considered parody. That turns in large part on whether a reasonable person would have realized the emails were not actually from the professor, as the jury in Hustler Magazine concluded that a reasonable reader would not have thought the Falwell interview to have been genuine.Yes, that sums up the issue pretty well.
Background here and links.