How do you dress for church?

There was a young man 18 -20 years old in church today wearing a blue polo shirt and shorts that covered no more than tennis shorts would. I didn't think this was appropriate for coming to church in. They young man is a very attractive person and doesn't need to dress this way to get attention. He was there with his sister, mother and grandmother. I am in my mid 20's so I'm not what would be considered an old person.