Spag head or spaghead is derived from "spaghetti head."
One who has many thoughts or ideas, personal or work related, running through one's mind.
She was a real spag head. She had alot on her mind and seemed to need a way to organize her thoughts and ideas.
An annoyingly smart person.. a person who over-uses the spelling and grammar rules.
Fred: Hey, how's you?
Fred: Aint got no money today mate, sorry
Bob: I think you mean "I haven't got ANY money"
Bob: Learn your spelling and grammar!
Fred: Shut it, spag head!!