Adam's off ox

Adam's off ox

An unrecognizable person or thing. “I wouldn't know him from Adam's off ox” was the equivalent of the contemporary “I wouldn't know him from a hole in the ground.” Since horses and other beasts of transportation and burden are handled from the left side, the left side is referred to as their “near side” and the right side their “off ” side. Not to be able to distinguish between someone and the farther-away animal of the first man on Earth is indeed not too know very much at all about a person
See also: off, ox