Avoid Duplicate values for INSERT in SQL

  <?php 
mysql_query("INSERT INTO `users_badges` (`user_id`, `badge_id`, `badge_slot`) VALUES ('$my_id', 'VIP', '1')");
?>

I have this code to insert something in the table but every time if you visit the home page the same user gets the item dubplicated. How can I fix this.

So basicilly I want IF already you have VIP,the code doesn't have a value to avoid duplicate.