There must have been times when you were annoyed by a specific person and simply did not want them to DM you any longer. The good news is that you can prevent them from messaging you in two ways. The first option is to find their conversation, tap the "information" icon, and then "report" the conversation. After that, users will be unable to send you Twitter Direct Messages unless you initiate a conversation first. The alternative to this method is to simply block that specific user. They can't message you or see your tweets this way.