Block A User:
You can now block specific users from viewing your profile, giving you +K or adding topics to your profile on Klout.  To block a specific user, view their profile and scroll to the bottom of the page and you will see a link that says "Block User" in the bottom left-hand corner.  Once blocked, you cannot view that user's profile and they will be unable to view yours.

Unblock A User:
To unblock a user, go to the upper right-hand corner of your screen where your name is located and select "Settings" from the drop-down menu.  Click "Privacy Settings" from the left-hand bar and click the "Unblock" button under the users name.