Region: US | Usage example: He couldn’t find his backside with both hands when we asked him to set up the new printer.

Couldn't find his backside with both hands

Meaning

Totally incompetent or confused.

Dismisses people who repeatedly miss the obvious.

Origin notes can vary by region and source; this page gives the commonly reported explanation and usage context.

American wry commentary on someone unable to complete simple tasks.

Used in US humor columns and roundtable talk in the early 1900s.