A person who is usually really stupid. Someone who makes mistakes and doesn't realize it. A person that is clumsy, stupid, or just plain weird. But you know, you can be a stupidhead and still be cool and fun. It just depends.
An Insult. A stupid stupidhead is someone who either looks like a stupid stupidhead, or is so stupid they have no clue that they are either acting like a stupid stupidhead or are a stupid stupidhead.