not know (someone) from a bar of soap

not know (someone) from a bar of soap

To be completely unaware of or know nothing about someone; to have never met the person indicated. My girlfriend got really excited when a movie star apparently walked past us, but I wouldn't know him from a bar of soap. Someone I wouldn't know from a bar of soap just contacted me online, claiming to be a distant relative.See also: bar, know, not, of, soap