[elizabeth52]

This is from the Emily Post Institute:

Men – Hats can be left on…
Outdoors
At athletic events (indoors or out)
On public transportation
In public buildings such as post offices, airports,* and hotel or office lobbies
On elevators

Men – Take hats off, including baseball caps …
In someone's home
At mealtimes, at the table
While being introduced, indoors or out (unless it's frigid!)
In a house of worship, unless a hat or head covering is required
Indoors at work, especially in an office (unless required for the job)
In public buildings such as a school, library, courthouse, or town hall
In restaurants and coffee shops
At a movie or any indoor performance
When the national anthem is played
When the flag of the United States passes by, as in a parade

Women – Fashion hats (not baseball-style caps) can be left on…
In someone's home
At luncheons, weddings, garden parties
At religious services
At a movie or any indoor performance
When the national anthem is played
When the flag of the United States passes by, as in a parade

Women — Take your fashion hat off…
Anytime it blocks someone's view, such as at a wedding or in a theater
Indoors at work
Women — Remove baseball-style (unisex) caps…
In someone's home
At mealtimes, at the table
While being introduced
In a house of worship, unless a hat or head covering is required
Indoors at work, unless required for the job
In public buildings such as a school, library, courthouse, or town hall
In restaurants and coffee shops
At a movie or any indoor performance
When the national anthem is played
When the flag of the United States passes by, as in a parade
*

*

(Cancer patients are exempt from hat rules. They may keep their hats or caps on at all times if they wish.)
*