Allow yours BuddyPress site members to create their usernames in site’s root. So that their profile URL appear as domain.com/username Just like Facebook & Twitter where profile URLs are facebook.com/username and twitter.com/username
You can easily do this by adding a single line code in your wp-config.php file or bp-custom.php file. So open your wp-config.php file and add the following code just before the ‘Happy Blogging‘ line:
define ( ‘BP_ENABLE_ROOT_PROFILES’, true );
This moves your members profile on root so that they appear as domain.com/username.