Liverpool slang. A derogatory term for a person with an oddly shaped, top-heavy, deformed or poorly hair-dressed head - resembling a scone. (The correct scouse pronunciation of "scone" rhymes with "one", not "cone" which is more typical.
A mix between a stoner and a pothead. A stonehead is a rare breed that is resulted from being a stoner with many pothead friends. A stonehead is usually aware of the name of what they smoke but not of what it is.
Julie can be such a stonehead sometimes. She's so unware of how good her stash is.