Hog   You cock your wrist and blast the CBD with noise. Startled knees snap back and walkers make mini-Maasai jumps into the air, land, utter and go on.   Your Harley has an extra fat black back tyre while Kawasaki riders have parked their bees in honey-comb rows for buzzing off at six past five.   The motorbike replaced the quiet Western Front dispatches horse. For life they kept the din down. Now when the Postie comes and goes you need to listen out.   You cock your wrist and blast the CBD with noise. But your sign language…