Couldn't find his backside with both hands
Meaning
Totally incompetent or confused.
Usage
Dismisses people who repeatedly miss the obvious.
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.
American wry commentary on someone unable to complete simple tasks.
Used in US humor columns and roundtable talk in the early 1900s.