You can block any user by going to their Klout profile, scrolling all the way down, and click the “Block User” link on the bottom-left corner, under their topics.
Once you click Block, another window will appear asking you if you are sure if you want to block that person. Click "Okay." That user will be unable to view your profile, give you +K, or interact with you or your profile on Klout in any way.
To unblock a user, you can go to your privacy settings at http://klout.com/#/edit-settings/privacy and click on "unblock" under the user's name.