Answer:
Jack Lemmon's character accuses Juror #3 as being a "sadist" when he proposes that 3 cares nothing for the facts of the case, and is bent on sending the kid to the chair for killing his father. It is reiterated throughout the film that 3 has more of a vendetta than the others in that he feels very negatively against a son being against a father, as this is something that had happened to 3 himself with his son, and he has yet to get over it.