I think the worst was the Dred Scott case where the US Supreme Court declared that no black could ever become a citizen of the United States.
Chief Justice Roger B. Taney wrote in the court’s majority opinion that because Scott was black, he was not a citizen and therefore had no right to sue. The framers of the Constitution, he wrote, believed that blacks “had no rights which the white man was bound to respect; and that the negro might justly and lawfully be reduced to slavery for his benefit. He was bought and sold and treated as an ordinary article of merchandise and traffic, whenever profit could be made by it.”
The next worst is the Citizen’s United case which has created a new class of citizen, the corporate citizen, with the right to spend unlimited amounts of money to promote their ideas. The first three words of the constitution are ‘we the people’. No mention of corporations there.