1. Download the plugin One Click Mark Spammer
2. Unzip the plugin and upload "one-click-mark-spammer"  to wp-content/plugins
3. Activate the plugin “One click Mark Spammer for BuddyPress”.
4. Now you can go and view the members directory and see the option to mark users.  Similarly visiting a users profile will show the links to mark spammer and so will the members list on groups page.