Usage: DCC CHAT NICK
  DCC CHAT initiates a direct client connection chat to the given
  nick, who must respond with DCC CHAT. This is the most secure
  form of communication available on IRC. Messages sent via a DCC
  CHAT connection are not sent through IRC, but are sent by a direct
  connection between your client and the remote client. Messages
  are sent over a DCC CHAT connection with /MSG =nick