Casuistry is argumentation that is suspect and sneaky. Politicians, lawyers, and car salesmen who make dubious arguments full of holes are guilty of casuistry.
Save this word for when you want to put down somebody else's line of reasoning: it refers to subtle but specious argumentation. It was formed from casuist (along the lines of sophistry and foolery), which can mean one who engages in such reasoning, though it originally meant someone who resolves doubtful cases by the application of principles. Casuistry is used to bamboozle people, so steer clear of those who practice it!