Definitions for so-and-so
Random House Webster's College Dictionary
a person or thing not definitely named.
a bastard (used as a euphemism).
Origin of so-and-so:
rotter, dirty dog, rat, skunk, stinker, stinkpot, bum, puke, crumb, lowlife, scum bag, so-and-so, git(noun)
a person who is deemed to be despicable or contemptible
"only a rotter would do that"; "kill the rat"; "throw the bum out"; "you cowardly little pukes!"; "the British call a contemptible person a `git'"
Some thing or things.
He will tell you to do so-and-so, but read the instructions first, anyway.