This question probably eliminated everyone else except the special lady of my dreams, so don't feel too bad. The human body is a precious gift from God, our Creator. It should always be treated with the dignity and respect befitting such a gift, so respectful and tasteful dress is always in order, not only in public, but in private as well. The woman I marry will be such a holy person that she will be deserving of seeing me nicely dressed from the moment I first stand before her in the morning until the time we go to bed. I hope she'll feel the same way about me. I'm not talking about a suit and tie or a ballroom gown here, but just old-fashioned "adult" dress. That means a dress shirt, dress pants, and dress shoes for a man-- and a nice blouse, dress slacks, a long, modest skirt or dress, and dress shoes for a woman.
Moreover, dress does influence the way people behave-- see the 1956 Warner Bros. short Bugs Bonnets for examples. Besides, jeans, sneakers, sweat pants, shorts, miniskirts, and the like are just too cultural for a hopelessly countercultural person such as me. They are the symbols of a culture gone bad-- certainly not consistent with Christianity. Just as we have sacraments (very important signs of God's grace such as the Eucharist and confession) and sacramentals (less important signs of God's grace such as a Miraculous Medal or holy water or oil) we have what I call "anti-sacramentals"-- signs of the sin that pervades the world today. What most people today consider "casual" or "comfortable" clothing clearly falls into the category of an "anti-sacramental." It says, "I belong to the world," instead of "I belong to God."
A common complaint leveled against this philosophy is "It's what's inside that counts." (Also expressed as "What's in the heart is what counts.") The flaw in that condemnation is the underlying, unstated assumption that what people wear has absolutely nothing to do with their values, as if certain people are born wearing jeans and they have no control over it. Clothes are not an accident of nature like height, eye color, or hair color (things you won't see discussed on this web site, by the way). People choose what they wear each day, usually from clothes they chose to buy when they were in a clothing store shopping for them. I believe that that choice reveals something important about the person making the choice-- what's inside. Scoff if you wish, but clothes don't just happen to people.
I know, in the twenty-first century, "nobody" dresses as nicely as I've suggested-- except for my wife. I only need one, after all.