plucked me ope his doublet "Pluck" means "pull," especially quickly or with a jerk. "Ope" means "open." The "me" adds the meaning of "for my benefit," but Casca is being sarcastic. He means that, in order to make a big impression on the crowd (including Casca), Caesar melodramatically plucked open his jacket.

Also, a "doublet" is a tight-fitting jacket of a type that was worn by almost everyone in Shakespeare's time, but by no one in Caesar's time.

  DOUBLET

TOGA