Ne pas avoir les yeux en face des trous

Literally: Not to have one's eyes lined up with the holes

Example: “Désolé pour la faute de frappe, je n'avais pas les yeux en face des trous ce matin.” — Sorry for the typo; I was barely awake this morning.

Origin: The morning after a bad night, or a good one, the eyes are open and demonstrably not working: you walk into the dog, you catch the door with your shoulder, you pour the coffee alongside the cup. From the 17th century French said such a person a les yeux de travers, had their eyes on crooked. This phrase, attested in 1925, takes the same joke further and proposes that the eyes are not sitting properly in their sockets at all — not lined up with the holes provided. Gaston Esnault argued the holes are the eyeholes of a mask being worn, which would also impair the view but adds nothing to an image that already explains itself, and no other source backs him. The second sense follows from the first: anyone who fails to notice a thing in plain sight gets the same diagnosis, whatever time of day it is.