Noun. Person of questionable intelligence who appears to be crazy or unaware or both, usually existing in the outskirts of society; different in a way that indicates insanity. Used in civil conversation, the word can be either negative or positive depending on the context. It is similar to the word "weirdo."
That guy is a complete whacknut for attempting to jump a valley on a dirt bike without ever having ridden one before.
by Gov540 September 3, 2013