not know sb from Adam

to have never met someone and not know anything about them

根本不知道(某人)，与(某人)素不相识

亚当是《圣经》中上帝创造的第一个人，所以from Adam这里就理解成了从亚当那个时候，也就从来都没认识过，对应中文里就是这个“素”字。只不过是一种更生动的表达。

Why should she lend me money? She doesn't know me from Adam.

她怎么会借钱给我?她根本不认识我。