This is from the blog Modern Vintage Girl.
"With my recent fascination and obsession with hats I’ve been looking at hat etiquette for both men and women. It’s actually quite different with men being expected to follow more rules...
A few sources have suggested that the difference is to due with the construction of the hats and how women’s hats where normally attached with hat pins and had more embellishments which made them harder to carry/take off.
Women are not required to take their hats off when going indoors, as they are a part of their outfits, however they can choose to do so.
Women can wear hats at formal teas, luncheons, and wedding ceremonies/receptions.
Women do not need to remove hats for the national anthem, unless they are men’s style caps, however they can choose to do so.
Women do not need to remove hats when in a restaurant, however they can choose to do so.
After 6pm cocktail/hats with small brims are appropriate. Examples of other appropriate head wear for evening are: fascinators, cocktail hats, Veils, combs, scarves as a headband.
Women are not required to remove hats in churches or other places of worship.
Women do NOT wear hats when:
Their hat might block someones view at the theatre.
When at work in an office.