Don't know if it really is where the expression came from, but I had always used the term "didn't know squat". A few months ago I was reading a story about a ship's captain who ran aground in a channel because he hadn't calculated for squat, which if I recall correctly, is the compression of water because of the weight of a ship. All of a sudden the lights went on for me.

According to a small book I have called West Coast Words by Tom Parkin, "Ants in your pants" or "antsy" supposedly originated from the habit of loggers putting their clothes on ant hills so that the ants would devour the crumbs (lice) Old style dry cleaning.