Code:
define('DISABLE_HOOKS', true);
Simply place that in your config.php for vBulletin (./includes/config.php), it'll disable all your plugins, once do head into the Admin CP and uninstall vB Optimise product, you won't need to delete the vB Optimise files to remove completely, but your safe to do so after the product is removed.
After that, simply remove the line from config.php and your products will work again