There are two ways (that I know of) to do this.A few extra steps that were left out by Vicki. Mods - never mind! Please close thread before more sidebar is added.
1) As Vicki said, click on the user's name and select View Public Profile. When you get to their profile page, under their name you'll see a drop-down link for Send Message, and next to that one for User Lists. Select the latter, and from the drop-down menu select Add to Ignore List.
2) Alternatively, on the left hand side of this page, under Main Menu, select User CP. This takes you to your User Control Panel. On the left hand side of that page, under Your Control Panel look down under Settings and Options. The last link is Edit Ignore List. Select that, and it will take you to a page where you can add members to your Ignore List. Originally Posted by Fratelli