Use format_username in theme_commerce_wishlist_user_wishlist_page_title()

As the comment above theme_commerce_wishlist_user_wishlist_page_title() already states, you might want to use the user's full name. The Drupal format_username() function is designed to show a formatted username and allows hook_username_alter (used by modules like Realname) to output a name other then the user's name property.

Proposition:

function theme_commerce_wishlist_user_wishlist_page_title(&$variables) {
  global $user;
  if ($user->uid == $variables['account']->uid) {
    return t('My wishlist');
  }
  return t("@name's wishlist", array('@name' => format_username($variables['account'])));
}