Principem populi tui non maledices. Acts 23:5
Saint Thomas says that normally a subordinate should not correct his superior. He can do it only when he must do it, only when necessary, and then, only with the greatest deference.
Detraction is the sin of unnecessarily exposing the sins of another.
Calumny is spreading lies about another.
Those sins, committed against one's superior, would be aggravated by being a sin also against piety, the proper respect due to one's superior.