pronoun , informal Someone whose name is not given. Don't tell me what so-and-so thinks. Tell me what you think.
n. , informal A person of a special kind and usually of a very bad kind. This word is used in place of a more unacceptable word or swear word. I wish that old so-and-so who thinks digging is easy work was right here digging now. He called me a dirty so-and-so and I hit him in the mouth. Sometimes used in a joking way. Peter met his friend John and said, "Hello there, you old so-and-so."