(perhaps there's explicit church teaching on this, but I'm unaware of it.)

“Women and girls who wear immodest clothes are to be prohibited from Holy Communion and from the office of sponsor in the sacraments of Baptism and Confirmation, and in certain cases, they are to be prohibited even from entry into the church.”

2. This topic was created to demonstrate yet another piece of evidence that the SSPX has completely changed its tune on this topic. All the SSPX priests used to preach that women must dress modestly, which excludes slacks, shorts and pants. The new, younger priests counsel things in the confessional like "wear however short a skirt your conscience will allow".

When I was involved with the SSPX 20+ years ago, only a handful of SSPX priests were saying that modesty for women excluded pants and slacks in public. I don't know why you think that was "all" SSPX priests.

Attire at Church naturally has higher standards - for men and women - than attire in public.  The Marylike standards say "slacks and jeans are not to be worn at church".

I meant explicit teaching on *what* constitutes immodesty, not on the immorality of immodesty.  Though maybe the other post you made answers that question.  

What I quoted in my first reply was Pius XI’s teaching on what constituted modest dress. If it doesn’t fit that standard, it can be considered immodest.
This was issued in 1930. Imagine what he would say about women’s dress today.

Does our guardian angel not see us at all times or not?  Is purity and modesty for God?  Or is it just for others?

Obviously its to honor God in the sense of not causing other humans to stumble and such.  But if its *directly* for God, our Guardian Angel, etc. then why would this not rule out things like showering nude and such?

I'm not trying to be difficult here, just trying to understand some of the reasoning.

We are both body and soul. We have to take care of our body by eating, drinking, health and cleanliness.  Outside of this, immodesty can come into play, even when alone.  Can the devil not tempt us to sensuality when alone?  So immodesty when alone can lead us to fall into sin.

Adam and Eve were married when they sinned in the Garden.  However their sin against God caused them to realize their nakedness in His sight, even if they didn’t realize it as a married couple.  So we can say that modesty is not ONLY for our neighbor, but also for God.  For we are temples of the Holy Ghost and must adorn our selves with the proper respect, even when alone.  

Immodest fashions and the sins of impurity it results in, probably more than any other single vice, is what has caused even formerly Christian societies to turn almost pagan or neo-pagan again. One of the worst sins of our times, which Our Lady of Fatima specially stepped down from Heaven to condemn. The Popes, especially Pius XI and Pius XII, have often deplored this sin and have set objective standards of modesty for both men and women that should be followed. Reverend Father Bernard Kunkel, who died in 1969, was a tireless crusader against immodesty.

"True traditional Catholics, mindful of the virtues of Christian modesty and purity, refuse to be stampeded by "the crowd" into accepting the hedonistic fashions. They know that the Blessed Virgin Mary will never approve of these pagan styles which are so contrary to Christian Tradition on modesty ...

Our Blessed Mother knew in advance the moral havoc that would follow the introduction of these unholy fashions. This is why she came personally at Fatima in 1917 to forewarn us. At the same time she gave the answer in advance to the question, "Is it a sin to follow these fashions?" To little Jacinta, aged seven, Our Lady entrusted this prophecy, which embodies her theology on the modern fashions: "Certain fashions will be introduced that will offend Our Lord very much."...

To emphasize still more the seriousness of "certain fashions", Pope Pius XII asked the Sacred Congregation of the Council to make a forceful appeal to all Catholics, but especially those in authority, to "leave no stone unturned which can help remedy the situation." Thus, he repeated the action of his predecessor, Pius XI, who had asked this same Sacred Congregation to send out the "Special Instructions" in 1930 directing that the Roman Standards of modesty in dress (Marylike Standards) be followed.

Pre-Requisite For the Triumph of Mary's Immaculate Heart

How can we expect Mary's triumph and world peace in an unchastened human society? And how can the reign of purity be established as long as these "certain fashions" continue to fan furiously the flame of passion in the hearts of men? Is it not evident from Our Lady's messages at Fatima that modesty in feminine attire is a prerequisite for Her triumph and for world peace?

Let's use our God-given faculty of reasoning. Our Lady tells us "Men must cease offending God...." In the next breath, as it were, she reminds us that one way in which God is offended "very much" is by those "certain fashions." The conclusion should be plain. These semi-nude fashions retard Mary's triumph, and are one of the chief causes bringing the world to the brink of annihilation.

Our Lady further revealed that "More souls go to Hell because of sins of the flesh, than for any other reason." Who can count the millions of mortal sins of the flesh that are daily occasioned by immodest attire-evil thoughts and desires, touches, impure embracing, kissing, raping, etc. How can the Immaculate Heart of Mary triumph as long as "more souls go to Hell" through shameless fashions?

Again, a Christian society would never tolerate the current flood of indecent literature, movies, and television if it had not first tolerated the public appearance of semi-nude women and girls IN THE FLESH."

When immodesty appeared in bad magazines etc, a Christian society should have confiscated those bad books and publicly burnt them; and likewise immodesty in other media including newspapers, the internet, TV anywhere else should never have been tolerated but should have been rejected from the start; to refuse to prevent evil is to allow it to spread, and when morals are corrupted, faith will always be in danger next. But that didn't happen because, as Fr. Kunkel says, such public sins were already tolerated even in the real world already. The Saints say sins against purity often soon thereafter lead to sins against faith.

"Listen to the Virgin Mary's pleas for "prayers and sacrifices." There can be no doubt that one of the sacrifices that is very acceptable to Our Lady is the sacrifice required to become ever more Marylike ourselves; and to promote energetically in others the "Marylike Way of Life'' which will restore Marylike chastity and modesty to the world. This will hasten true world peace, which is promised only through the Triumph of the Immaculate Heart of Mary."--Rev. Fr. Bernard Kunkel

There's an Act of Consecration to the Immaculate Heart for Purity on the Salve Regina page we could make. If others tempt us, we should stay away entirely from bad influences. And we should avoid being a stumbling block to anyone by always dressing modestly.

The power of sin can be overcome by prayer and by Sacramental Grace. The youth especially need constant reminders of the necessity of striving after the virtue of purity and its necessary connection with behaving and dressing modestly from their Priests.

WOW! That's modesty up over!

Obviously its to honor God in the sense of not causing other humans to stumble and such.  But if its *directly* for God, our Guardian Angel, etc. then why would this not rule out things like showering nude and such?

I'm not trying to be difficult here, just trying to understand some of the reasoning.

The Guardian Angel line doesn't really make sense and sounds vaguely Gnostic to me. The Apostles are often depicted as having fished topless, due to the heat and the sweat from the intensity of the work. Were their Guardian Angels scandalised? This assertion being thrown around here that modesty has nothing to do with the audience is a little strange. Yes it's uncivilised and shameless if you're just strolling around your house completely naked or just in your boxers, even if no one's around. And you could call that an issue of modesty I guess. But after the most basic level of covering up it's completely dependent on the audience. Taking your shirt off while you're overheating from hard work in the sun, your only company being other men, - there's nothing wrong with that. Doing so for no practical reason around women is obviously immodest. I personally wouldn't go around in front of women in just my boxer-shorts and a t-shirt, but why exactly would that be a problem while sleeping in my own bed? My Guardian Angel will already have to see me when I'm getting changed or in the shower. Some people even go to the ridiculous extreme of saying Guardian Angels are scandalised by babies being left naked for a moment while being changed. Ridiculous!