Situation: woman wears shorts out to a grocery store.
Someone who had issues with purity: she's trying to seduce people and ultimately to fornicate. (could be from a woman who used to dress provocatively to seduce people or from a man who used to indulge in pornography)
Someone without such issues and no understanding regarding the moral aspect of immodesty: it's just a normal thing to wear, comfortable, especially when it's hot out.
Objective truth: Is she trying to seduce people? Maybe she is and maybe she isn't. I don't know and can't judge. While I can judge that it's objectively wrong to dress that way, I cannot judge the person's interior dispositions. THAT is what Our Lord means by "do not judge". It does NOT mean we can't know that WHAT she's doing is objectively wrong. But we cannot judge their interior dispositions. We don't know what graces they've received or haven't received. We don't know whether she's been informed about the matter (very few people in society have). So the truth is in the middle, as usual. Conciliar Modernists tend to say that "do not judge" means we can't judge that WHAT she is doing is wrong, whereas Traditional Catholics sometimes overreact and claim that we can judge their interior dispositions. So, for example, the Conciliarists may conclude that "we can't judge that sodomy is sinful", whereas a Traditional Catholic might judge the person harshly. In reality, we don't know why the sodomite turned out that way. Was he abused as a child? Did he have some hormonal imbalance? Was he raised to think that sodomy was OK? What graces did he receive or not receive? But for the grace of God, there we go as well. We thank God that we're not afflicted with the tendencies that lead to sodomy, but do not glory in it as if that were our own accomplishment rather than the grace and mercy of God alone. When we realize that EVERYTHING in us that is good is in fact not us but God, then we can become charitable and humble. St. Paul gloried only in his infirmities, because those are all that he could rightly call his own. Everything good in him was not his to boast of, but was from God and a free gift from God. THAT is why the greatest saints believed (and not just feigned) that they were the greatest of sinners. They realized how many graces they had received and how many they had wasted, and yet always gave their neighbor the benefit of the doubt, assuming that they hadn't received the same graces. Everything good in me: God's doing. Everything bad in me: that's me there. That's why Our Lord reminded us that compared to God we are all "evil", referring to the "you who are evil". Forgive me from waxing philosophical for a moment. But we creatures, contingent beings, are a mixture of "is" (good) and "is not" (evil). God IS and evil IS NOT. Pure evil does not exist. That's from the great thinking of St. Augustine. So in this mixture of "is" and "is not" that we all are, the "is" part is just God Himself, and the "is not" is our own contribution to the equation.
And this is why pride is the greatest sin. We appropriate to ourselves that which is God's. We take credit for any goodness that God has generously shared with us. That's also why vanity and immodesty is a terrible thing. Women who are vain and immodest want to take credit for possessing a beauty of themselves that is merely a gift from God and a sharing of Himself with them. We men who are on the opposite side of that err by attributing that beauty to the creature rather than to the Creator and desire also to possess it of ourselves instead of attributing it to God and recognizing that it is from Him and is Him.