perfect stranger
Someone with whom one has absolutely no previous association. My mom and dad didn't come to see our son until he was nearly three years old, so, to him, they were perfect strangers! She thought it was terribly funny to go up to perfect strangers and begin conversations with them as if they had been lifelong friends.
perfect stranger
and total strangerFig. a person who is completely unknown [to oneself]. I was stopped on the street by a perfect stranger who wanted to know my name. If a total stranger asked me such a personal question, I am sure I would not answer!