Code to add to the beginning wp-config.php that causes WordPress to shutdown without ever connecting to the database if someone tries to login with the username "admin"

wp-config.php

<?php

// ** Reject Bad Username ** //
/** As described on http://salferrarello.com/wordpress-bad-login-attempts/ **/
$bad_user_names = array( 'admin' );
if (
	isset( $_POST['log'] )
	&& in_array( strtolower( $_POST['log'] ), $bad_user_names )
	&& false !== stripos( $_SERVER['REQUEST_URI'], 'wp-login.php' )
) {
	die();
}

// ** MySQL settings ** //
/** The name of the database for WordPress */
define('DB_NAME', 'example');
...