utter stranger; mere passerby; outsider
A set phrase emphasizing that someone is a complete stranger with no connection to oneself, often used in contexts of indifference or lack of obligation.
He is nothing more than a complete stranger to me.
困っている人を見ても、路傍の人のように通り過ぎてはいけない。
Even if you see someone in trouble, you shouldn't just pass by like a mere passerby.