Doesn't know his backside from a tomato can

Meaning

Completely clueless about a subject.

Usage

Describes ignorance in a colorful, folksy way.

Origin & History

Origins and dates here are approximate summaries. Many idioms have disputed or unknown origins, and not every date has been checked against a historical dictionary, so treat specific dates and stories as a starting point rather than a citation.

Frontier slang contrasting a clueless person with the obvious shelter of a tin can.

Found in Southwestern US newspapers and cowboy tales around 1900.