bbPress.org

I just added this on my test site:

add_action( 'wp_head', 'casiepa_add_noindex' );
function casiepa_add_noindex() {
  if ( bbp_is_single_user_profile() ) {
    wp_no_robots();
  }
}

And I when I go to the profile of a user (in my case /forums/users/user1/), I now correctly find:
<meta name='robots' content='noindex,follow' />

Could you have a check on your side?