He constantly says that Brutus was an honorable man when he means just the opposite.
In his speech, Antony keeps telling the people about bad things that Brutus has done, each time ending by saying that Brutus is an honorable man. By doing this, Antony is highlighting the fact that he thinks Brutus acted dishonorably. The people agree with him because of how effective his irony is. This is shown by their anger at Brutus and the conspirators.