"It is acceptable for women to wear hats in Christian churches, (it was once required, but the custom has all but disappeared) but disrespectful for men to wear them."
http://www.askandyaboutclothes.com/Clothes%20Articles/etiquette_for_hats_and_caps.htm
I remember (yes I am older than dirt) when hats were required in all services, especially Catholic. If you didn't wear one, someone handed you bobby pins and a hankie to fasten to your hair.:lol
Today, the only hats I see in a church crowd are the african american churches, who do a beautiful job of dressing for their services. Sadly, my own religion has gone to extreme dressing down, to the point that the priest reminds people that the revealing t-shirts and short shorts are not welcomed.