not know someone from Adam
Fig. not to know someone by sight at all. I wouldn't recognize John if I saw him up close. I don't know him from Adam. What does she look like? I don't know her from Adam.
know (someone) from Adam, doesn't/not to
Not acquainted with someone. The Adam referred to in this mid-nineteenth century term is the first human being according to the Book of Genesis. One writer suggests that the inability to recognize Adam is the height of foolishness, since he had no name and wore only a fig leaf, but this point does not seem particularly relevant. The French have a similar saying that includes Eve as well (“Je ne connais ni d’Eve ni d’Adam”).
not know from Adam
See know from Adam.