When you're logged in, look at the top-right of the screen. Click on the downward-pointing triangle to the right of your name, and choose "Manage Ignore Prefs". From there, you'll see the Ignore screen, and you can type in a username, (you may want to have that copied to clipboard before you begin), and click Add. Note you must also choose exactly what you want to ignore, by ticking the three selection boxes to the right of the Add box.