/**
 * Implements hook_username_alter().
 * The main role is considered to be the one with the higher RID.
 */
function username_prefix_username_alter(&$name, $account) {
  global $user;

  // Retrieve user roles to understand the correct order.
  $site_roles = user_roles();
  if (!empty($account->roles)) {
    $user_roles = $account->roles;
  } elseif($cached_roles = &drupal_static(__FUNCTION__)) {
    if (!empty($cached_roles[$account->uid])) {
      $user_roles = $cached_roles[$account->uid];
    }
  } else {
    global $user;
    if ($account->uid == $user->uid) {
      $user_roles = $user->roles;
      dpm($user_roles, 'ZZP');
    } else {
      $user_obj = user_load($account->uid);
      $cached_roles = array();
      $cached_roles[$account->uid] = $user_obj->roles;
    }
  }
  $site_roles = array_reverse($site_roles, TRUE);

  // Goes through every site role, in order or importance, and check if the user has it.
  // Then check if there is a prefix for the specific role. If not, keep checking...
  foreach ($site_roles as $key => $role) {
    if (!empty($user->roles[$key])) {
      $selected_role = $role;
      $selected_role_key = $key;
      $role_prefix = variable_get('username_prefix_' . $selected_role_key, '');
      if (!empty($role_prefix)) {
        $name = $role_prefix . $name;
        break;
      }
    }
  }
}