The correct option is
B Discourtesy
The word 'chivalry' refers to courteous behaviour, especially that of a man towards a woman.
Option A, dishonesty refers to deceitfulness shown in someone's character or behaviour.
Option B, discourtesy refers to rude and inconsiderate behaviour.
Option C, disobedience refers to failure or refusal to obey rules or someone in authority.
Option D, disaffection refers to a feeling of dissatisfaction, especially with people in authority or people in control.
Thus, according to the meaning, the word 'discourtesy' is the most opposite in meaning from the word 'chivalry'.