Explanation: Just a silly joke about the supposed tendency of Brits to want everything in order ("Can't park there", "Queue up", "Got a license for that?") applied to the Roman presence in ancient Britain. Of course, at the time, it was the Romans who loved having things according to nice, orderly plans and rules.
Featured is a Roman caroballista, a cart-mounted light artillery piece. 'Brittunculus' is a Latin term meaning, roughly, 'Nasty little Briton' - '-unculus' is just a diminutive form for nouns, but the usage of the term 'Brittunculus' is derogatory.