One day you will be called upon to break a big law in the name of justice and rationality. Everything will depend on it. You have to be ready. How are you going to prepare for that day when it really matters? You have to stay "in shape" so that when the big day comes you will be ready. What you need is "anarchist calisthenics." Every day or so break some trivial law that makes no sense, even if it’s only jaywalking. Use your own head to judge whether a law is just or reasonable. That way, you'll keep trim; and when the big day comes, you'll be ready.
For the quotation's context, which Godwin's Law aficionados should appreciate, go here.
We have a review of Two Cheers in the works; in the meantime, you can read my review of Seeing Like a State here and Tom Palmer's review of another Scott book here. More Scott cameos in Reason can be found here, here, here, here, and here.