A bathroom is referred to as a בית הכסא, because there is a mitzvah to cover ones waist, as quoted in the pasuk in sefer Devarim (23:14), and the word כסא (with a סגול under the כ and ס)means cover. (In those days there was no chair or seat in the bathroom they sat on a stone). The Torah is teaching us that even in the bathroom a place with waist and dirt one must act with proper צניעות, and not uncover from themselves more than they need to in order to not get dirty, and not to remain uncovered for more time then needed. This is because a person must give themselves the self- dignity that they deserve. (The measurements given in halacha for how much to uncover in the bathroom was for those days, but nowadays the bathrooms are closed in rooms and not in open fields. Therefore one can uncover more, but only what is reasonably needed).