Responsa על בבא קמא 65:10

Q. B swore to leave all his disputes with A, to C and D for arbitration. Subsequently, B vilified A's father calling him shameful names, to which A retorted: "not my father, but your father". B became enraged at the insult to his father who had been a scholar and a sage. Both fathers were dead at the time. Now B demands that A be duly punished for vilifying a scholar after his death.
A. We have no right to adjudicate fines, but a court is permitted to take emergency measures whenever necessary. However, if A will take an oath to the effect that he did not fully understand the charge B had made against his father but automatically replied, "your father", he will be free from obligation. Moreover, B must leave this dispute also to C and D for arbitration. He can not press this charge separately without transgressing his oath. On the other hand, since people customarily and automatically reply "your father" whenever someone vilifies their father, B deserves greater punishment than A since he was the first to use vile language. In any event, both A and B should appear before a scholar seeking atonement for their sin of having vilified the dead.
SOURCES: Cr. 298.