In this week's Parsha, we read that after Yosef demands from his brothers that they bring their youngest brother to Egypt, the rest of the brothers go back to Yaakov and ask his permission to let Binyamin come with them to Egypt. Yaakov, however, denies their request by saying that "יוסף איננו", Yosef is not with them, "ושמעון איננו", and Shimon is not with them, "ואת בנימן תקחו", and now you will take Binyamin (בראשית מ"ב:ל"ו); perhaps something bad will happen to him. In requesting that Yaakov reconsider, Reuven says to his father, "את שני בני תמית...," "my two sons you should kill...," meaning that Reuven was willing to lose his own sons if he wouldn't bring Binyamin back to Yaakov (שם פסוק ל"ז). Rashi (לפסוק ל"ח שם בד"ה לא), quoting the Midrash, comments that Yaakov didn't accept Reuven's request or his guarantee, saying "בכור שוטה הוא זה", "this first born son (Reuven) is speaking as a fool," because he is saying that I should kill his two sons, when in fact his sons are my sons too; they are not his sons only and not mine, why would I kill them? Many Meforshim are thus troubled by this "suggestion" made by Reuven. Why would Reuven make such an obviously absurd offer?
The Chasam Sofer, in his Sefer Toras Moshe on Chumash, does not accept that Reuven even entertained the possibility of having his sons killed. He thus explains Reuven's request in a completely different manner. He says that Reuven really meant to say not that Yaakov should kill his sons, but that he should take away their בכורה, their rights as descendants of the first-born. He proves this idea by referring to a Posuk later in the Torah that says "ויהושע וכלב חיו...," "Yehoshua and Caleiv lived..." (במדבר י"ד:ל"ח), which Chazal say means that they inherited their portion in Eretz Yisrael. We thus see that the word "חיו," "lived", refers to inheritance; so too we can say that the reference to death in our Posuk (בראשית שם) could mean a deprivation of inheritance. The Chasam Sofer brings a further proof to this interpretation from a Gemara in Bava Basra (דף קכ"ו:) which calls a בכור who doesn't receive a double portion a בוכרא סכלא which the Rashbam (בוכרא שם בד"ה) says means a "בכור שוטה", meaning an abnormal בכור, at least in so far as inheritance goes. This may therefore substantiate this view that Reuven's presentation and Yaakov's response had to do with the inheritance of the first-born. The term "בכור שוטה," however, remains an uncomplimentary one, since it implies that something is wrong.
Another illustration of this last idea that the term "בכור שוטה" used by Yaakov has to do with an abnormality, not necessarily an intellectual deficiency, is found in the Gemara in Sukkah (דף ל"ב:) which teaches us that we can't use a "הדס שוטה" as one of the four Minim on Sukkos. Many Rishonim consider such a הדס to be of a different species, and not a real הדס. A regular הדס has at least three leaves coming out of the same source in numerous places along the entire branch. A הדס שוטה, however, has two leaves coming out of one source and one coming out a little higher or lower. Since it is not straight, it is considered incomplete and invalid for the Mitzvah. This is similar to the בכור שוטה who is not complete and loses his double portion of the father's inheritance. This seems to imply that the term שוטה is applied to something - or someone - that is not quite straight or complete.
We can see from this concept an important Mussar lesson. We must live our lives on the straight path and be complete Jews, serving Hashem in every way so that the term שוטה will never be applicable to us, with any of its possible meanings.