I'm vindicated once again
When questioned about appropriate dress for attending Liturgy, my standard answer (without much thought) has been "Dress as if you are attending a wedding at which you are not the groom or bride." But look at what Jesus says:
Mat 22:11 "But when the king came in to look at the guests, he saw there a man who had no wedding garment;
Mat 22:12 and he said to him, 'Friend, how did you get in here without a wedding garment?' And he was speechless.
Mat 22:13 Then the king said to the attendants, 'Bind him hand and foot, and cast him into the outer darkness; there men will weep and gnash their teeth.'
Mat 22:14 For many are called, but few are chosen."
Now, I know that the parable is not about dress. But one can make dress be about the kingdom of God. The external sign of me dressing for a wedding is a reminder that I need to get my internal house in order.
God isn't hurt by my being sloppy, but I certainly can be hurt if sloppy dress mirrors a sloppy inside. Now, given the close unity of body and soul, it is likely that for almost all of us, clothes do indeed make the man (or woman). What you wear reflects and helps create what you are.
So ditch the jeans and t-shirts for Mass.