When someone is said to "run roughshod" over something, it means they have acted with complete disregard for any rules or conventions. There are many synonyms for this phrase, including "trample," "bulldoze," "stomp," or "ride roughshod." These words imply a sense of aggression and carelessness, as if the person in question is not concerned with the consequences of their actions. Other potential synonyms might include "steamroll," "flout," "disrespect," or "override." Ultimately, any of these words could be used to describe a person who acts without regard for the rules or conventions of a particular situation, often causing harm or creating chaos in their wake.