In the Block section of the Configure Site > Social Networking page, you can choose to allow members to block other members.  Like other features, you can choose the button images to block/unblock a member, and how to display the block/unblock image/text button.

If you use the Block feature, it will display on the Public Profile page of a member automatically, if you are using the Default page type format, and the website visitor viewing the page is a logged in member, and not blocked by the member.  On their Edit Profile page, each member can view members they have blocked and choose to unblock them if they would like on this page as well as the member's Public Profile page.