“UShifatitem Tzedek Bein Ish U’Bein Achiv U’Bein Geiro”, you shall judge righteously between a man and his brother and his Ger (Devarim 1:16). In one pshat, Rashi says that the word “Geiro” does not mean convert, but rather his opponent. The Sifri says that it means his father-in-law. Where does a father-in-law come into the picture and why does the Torah need to tell us this?
Rav Chaim Kanievsky answers that the Taz paskens (YD 241:2) that a son cannot take his father to court because it may cause his father to be cursed if he needs to swear. What the son should do suggests the Taz is to sell his claim to someone else who is halachicly fee and clear to sue his father.
Since the halacha is that when it comes to kavod, one is obligated to honor his father-in-law just like his father, you might think that you cannot sue your father-in-law either, therefore the Sifri tells us that unlike your father, you are free to litigate against your father-in-law and there is no problem of the issur klala.
Interestingly their was a famous court case where the Taz sued his father-in-law the Bach.
Rav Shmuel Berenbaum was fond of telling of the story how the Taz took his shver, the Bach, to a Din Torah. The Bach had promised had promised the Taz as part of his Nidunya that he would provide him with meat every day. When the Bach lost his money, instead of providing the Taz with a quality piece of meat which he could no longer afford, he provided him with the lung, which was far more inexpensive. The Taz demanded a good piece of meat claiming that lung was not called “meat”.
To help you understand who the Taz was, after fleeing the Cossack onslaught in which two of his sons were murdered, he lived in anonymity and poverty, earning a wage cleaning the Shul rather than revealing his identity although he was of advanced age and recognized throughout the Jewish world as a Gadol HaDor.
But he sued his own father-in-law for a good meat? Mi’ut Ta’anug, a bit of pleasure, says the Mishna. How much? As much as will help your body respond to your wishes to serve Hashem with every ounce of energy. The Taz was not willing to forego the minimal amount of extra learning he would lose by giving up his meat for lung, even if it meant suing his own father-in-law. And you could be sure the Bach was the proudest defendant to ever stand trial!
Pas BaMelech Tochal, a menu of bread and salt, says the Maharal MiPrague, should not stop you from learning Torah. However, if you have the resources, use them all. Not to indulge your appetite but to enable yourself to learn more Torah.