A person who tells the recipient of a gift what the gift is before the person actually receives it.
During the Christmas Holiday, the wife called her husbands place of employment looking for him. Despite knowing he had stepped out to buy his wife something at Tiffany's, the phone receptionist answered, "He's at Tiffanys shopping."
To which the wife responded, "He's going to but me something at Tiffanys!!!" A co-worker called the phone receptionist a "gift narc" for ruining the holiday surprise.