code: public void setMuted (Name username, boolean mute)
      {
          boolean changed = mute ? _mutelist.add(username) : _mutelist.remove(username);
          String feedback;
          if (mute) {
              feedback = "m.muted";
          } else {
              feedback = changed ? "m.unmuted" : "m.notmuted";
          }
  
          // always give some feedback to the user
          _chatdir.displayFeedback(null, MessageBundle.tcompose(feedback, username));
  
          // if the mutelist actually changed, notify observers
          if (changed) {
              notifyObservers(username, mute);
          }
      }
docs: Mute or unmute the specified user.