A drunk gets on a bus. The driver, impatient while the drunk fumbles in his pocket for change, drives off. As the bus starts rolling, the drunk reacts to the sudden movement by stumbling all the way to the back of the bus.
The bus stops at the next stop. He reacts by stumbling to the front of the bus. Still the drunk man is fumbling in his pocket for change. The bus jerks forwards once again, and the drunk stumbles uncontrollably to the back of the bus once again. Next stop, the same thing happens. In fact, every time the bus stops, the man staggers to the front. Every time the bus starts, he staggers uncontrollably to the back. A few stops later, the drunk starts to exit the bus from the front.
‘Hey, shouts the bus driver. ‘You didn’t pay your fare yet!’
The drunk, still reeling, shouts back, ‘Why should I?! I walked all the way!’