The Ignore list can be found on the Social tab in your UI. The default key shortcut to the Social window is O. The ignore pane, which will currently hold up to 25 names, has 2 buttons at the bottom, Ignore Player and Remove Player.
Ignore Player - This button brings up a box where you can type in the player name you want to ignore. Clicking the Accept button will add the name to your ignore list. Clicking the Cancel button will close the box without changing your ignore list. Using /ignore will block /say, /tell and all social channel comments from the ignored player.
Alternatively, you can add a player to your ignore list with the slash command /ignore. Use: /ignore <Character Name>
Remove Player - This button removes the selected player's name from your ignore list.