Not know (someone) from a bar of soap verb phrase idomatic
To have never met someone or to completely unknow anything about someone
Harry is really fond of Victoria but he doesn't know her from a bar of soap.
Last night, a man who I wouldn't know from a bar of soap started a conversation with me.
I wouldn’t know this girl from a bar of soap, but she insisted claiming that she was my distant relative.
To refer to an unfamiliar or faraway place.