Negro was a derogatory term used to refer to black people.
In 1941, the Nazi SS officer Koenig remarked that it was "quite a statement for a negro" when Clyde Langer told him that he did not belong in England. Clyde accused Koenig of resorting to name-calling and referred to the Nazis as "a gang of bullies, picking on others for what they look[ed] like." (TV: Lost in Time)
In Alabama in 1955, black people were often referred to by their white oppressors as "negroes". When the Thirteenth Doctor and her companions visited a diner in Montgomery, Alabama during this time, the waitress informed them that they "didn’t serve negroes", in reference to Ryan Sinclair, who flippantly responded, "Good, 'cause I don't eat them." (TV: Rosa)