Social media tools like Twitter have allowed people to express themselves in all new ways. But what are the limits of that expression? Are you allowed to say anything you want on Twitter? Most people would say yes.Twitter is protected under the First Amendment, they'll say. However, ask some lawmakers and police officers and the answer will vary. Over the past few years we've seen a number of people arrested for what they've tweeted. Some have been harmless jokes, while others were hardcore threats.

Last year, the NYPD asked Twitter to give up info on a user who threatened to carry out an Aurora-like shooting at a Broadway theater. Twitter refused to cooperate, so now the boys in blue are working to subpoena the social network. Another man recently plead guilty after being indicted for threatening to kill the president on Twitter in September. If you needed a reason to watch what you tweet, take heed from these examples.