He's that narrow, one eye would do him
A comic description of a very thin person - so thin from the front that a second eye would be unnecessary, since you could see the whole face with one. Used affectionately or with mild concern, never cruelly. Common variants substitute 'skinny' or 'thin' for 'narrow'.
Etymology
A South Armagh family phrase, structurally typical of Irish comic exaggeration: take a literal physical observation to a deliberately absurd conclusion. Similar Irish informal variants are widely heard ('he's so thin now the one eye would do him', 'she's that skinny one eye would do her') in slightly different forms. No single point of origin is recoverable; the construction is a folk template into which a particular speaker fits a particular observation.
In a sentence
"Did you see him at the funeral? He's that narrow, one eye would do him."
Historical notes
The phrase belongs to the body of Irish 'comparison comedy' - extreme physical observations made through a logical absurdity. The trick is the listener doing the visual maths: if a person is so thin you'd see all of them face-on, then their second eye, set on the other side of a normal head, becomes redundant. The line earns its keep because it works as concern dressed as a joke; the speaker is usually a relative or close friend, never a stranger.
Alternate spellings
he's so thin now the one eye would do him · she's that skinny, one eye would do her
Sources
- Local oral evidence, South Armagh (Patrick Hughes, family). · other