the first thing about (someone or something)

Any information at all about a particular person or thing. Typically used in negative constructions to indicate total one's lack of knowledge or experience. I don't know the first thing about computers, so you'll have to explain this to me really slowly. What's an attachment again? Geoff wouldn't know the first thing about how to take care of a baby. Thank goodness Frank is there to help babysit. Why do you presume to know what I would or wouldn't do? You don't know the first thing about me!