What is bein adam lechavro about not being tznius
1) Every bein adam lamakom has an element of bein adam lachaveiro in it, because klal Yisroel is one, and we are all affected by anyone sinning. Kol Yisroel areivim zeh lazeh.
2) Any aveirah done publicly has an even stronger element of bein adam lachaveiro, because it bothers people who are yarei shomayim, and has a negative influence on people.
3) Tznius in particular can be machshil men as well.