Tzniut - between man and God?

A student asks:
Are the mitzvot of tzniut considered bein adam l'makom or bein adam l'chavero? Is the focus of these mitzvot more about keeping a holy and moral environment or about individuals valuing the body that Hashem gave them? On a practical note, if someone were to violate the halachot of tzniut (they exposed erva in some way), would they have to ask mechila from everyone who saw them them, or only from Hashem?

This is a quick answer off the cuff, without consulting any sources. I was talking with my 10th graders about R. Saadya Gaon's idea that the 10 commandments are really categories, and every one of the mitzvot can be fit under one of those 10 headings. We then discussed specific mitzvot, and tried to figure out under which category each belongs. For example, we said korbanot fit under "Anochi Hashem"; damages for injuries under "lo tirzach." When someone brought up tzniut, one girl put it in jest in the category of "kibbud av va-em," which I found pretty funny. The serious suggestion, however, was "lo tinaf," that a lack of tzniut was somehow related to adultery or sexual immorality, which would correspond with your view that it's a bein adam le-chaveiro issue. My own opinion, which I said at the time, is that it fits under "Anochi Hashem," that a person is created in the image of God, and that we represent Him in this world, and are thus enjoined to present ourselves - and view ourselves - as dignified human beings. The image of God is our neshamah, perhaps our intellect as well, things that make us different from animals who are primarily physical, and that's why our clothing should reflect not our physical aspect, but our spiritual. A couple of nafka minas: how about men and tzniut? Well, if it's about dignity, then it applies just as much, and I know men who have standards of dress (for example - they won't wear shorts in public, or go without a shirt) which they view as tzniut for themselves. Another nafka mina: how do we act when we're alone? If tzniut is bein adam le-Makom, then we act with dignity then as well.