The word rank comes from a German word that was used to refer to someone tall, upright, or proud. But the English word had a more clearly negative connotation; it referred to someone who was too proud, someone who was haughty or arrogant – and that’s how Antony is using it here. But in Shakespeare’s day, rank had a second meaning. It described a swollen part of the body, which could be treated by draining the excess blood. So Antony cleverly combines both meanings. He’s wondering if Brutus and Cassius think there are other people who are so rank, or arrogant – like Caesar – that they must be bled, or killed, as Caesar just was.