1derogatory A person's head likened to a potato, either in appearance, as being large, bald, ugly, etc., or as implying stupidity.
Sometimes associated with Irishness.
2A person whose head is likened to a potato; a stupid person, a fool. Also: a person from an area known for the cultivation of potatoes, especially Ireland; (hence) an unsophisticated person from a rural area; a country bumpkin, a hick.
3US "Mr (also Mrs) Potato Head" noun and variants (a) (a trademark for) a children's toy consisting of plastic features, limbs, etc., intended to be stuck into a potato (or, in later use, a potato-shaped plastic body); (b) depreciative (a name for) a person regarded as ugly, peculiar-looking, or stupid.
Early 18th century. From potato + head.