People who wear a t-shirt to a nice restaurant or jeans to a wedding are either (a) ignorant of proper rules of decorum, meaning they weren't raised right or (b) making a childish statement: "look at me, look at me, I'm different!"
In either case, they're really not worth knowing. What other reason could they have for such behavior?
Their luggage was lost?
You just reminded me of my cousin's wedding. I had no shoes. We traveled for five hours and got there just in time to dress for the wedding and show up. When I searched our luggage for my dress shoes, they were not there. I was only nine or so, but it was very embarrassing.