When God looks at you, He does not see your clothes or any material possessions of this world; however, He does see straight to the soul and recognizes what your intentions are with the clothing you choose to adorn yourself.
If a hooker suddenly realized that she needed a new life in God but didn’t have better clothes to wear to church, don’t you think God would rather her come to church rather than let material objects keep her from Him?
Additionally, there are many harlots in the church that dress very respectably and yet go to church with intentions out of God’s favor. Don’t think for one second that her outward appearance fools God.
What you wear to mass has little to do with respect for God as much as it has to deal with respect for our brothers and sisters in Christ. I’d like to think that if someone truly care about God and His people, they would choose not to dress in a way that could distract from His message. It’s important for these people to be made aware if their clothing is distracting to their brothers and sisters, but we cannot allow ourselves to deny them access to God’s church based on our opinions of their attire as our God does not mind them there if their intentions in His church are well.
Even so, it’s important that we not be unreasonable in what we consider appropriate attire as people may feel turned away from the church if over-scrutinized, something I’m sure God would dislike more than bad clothes. Also realize that if we are in a mindset that would allow mere clothing of another person to distract us from God’s will, then maybe a more important thing we should consider is our current path with God and why we would allow material things to take us so easily from His focus.
( All of this also applies to life outside of church walls.

Maybe even moreso )