From Al Quran, Insya Allah
:salam2:
I really understand your problem brother, as i live in a country which has been contaminating by so-called "freedom of expression", thus many young girls and women here are wearing "unregulated" clothing, eventhough they say that they're muslims, big question mark ey..
Anyway, I turned to Qur'an to solve the problem, as stated in this ayat;
Audzubillahimishshaythoonirrojim
Bismillahirrohmaanirrohiim
(Surah 24; Nuur, ayah 31)
And say to the believing women that they should lower their gaze and guard their modesty; that they should not display their beauty and ornaments except what (must ordinarily) appear thereof;
If we see from other way around, from men point of view, by stating "they should not display their beauty and ornaments", it means that men are not allowed to gaze on women beauty and "ornaments" of their beauty, or women's "Aurat".
As for "Except what must ordinarily appear thereof", some ulemas here clarify that parts of women which ordinarily appear are their face expression (eyes, according to some) and their hands gesture.
It is common sense though, if you talk to somebody, man or women, normally we notice by looking their face, or eyes, expression and hands gesture. It's not common and not ordinary if you look at people's, say; neck, shoulder, hair, lips, nose, cheeck, bossom, or tights and others while you talking to them, some considered this as rudeness...
So, brother, if you in that kind situation again, try to focus with face expression through their eyes, not any part of the face, and hands gesture...
Hope it helps
Allah knows best
Wassalam