Ride roughshod over someone

Means to domineer, tyrannise or treat someone without any consideration and dates in this sense from the early 18th century. The origin derives from riding roughshod horses i.e. where horseshoes have nail heads protruding to provide better grip over difficult terrain. Warhorses often had spiked shoes for such terrain. To be trampled by such roughshod horses was a distinctly unpleasant experience, as infantry would find out when ridden over by such cavalry.