peanut head
/ˈpiːnʌt hɛd/slang (originally US )
noun
1A stupid or foolish person; also as a term of abuse. Compare pinhead, pea-brain, etc.
2A particularly small head. Also: a person with such a head, especially as part of a generally small or thin frame; frequently as a term of mild abuse.
Origin
Late 19th century; earliest use found in Ohio Democrat. From peanut + head.