Hi,
I was taught the same thing as I think the late Alabama coach, Paul "Bear" Bryant, was: when a man's indoors, the hat comes off. I don't recall any exceptions.
I mention Bear Bryant because he was famous for the trademark hat he always wore on the field:
There was a story which went around back then that when The Tide played in a covered stadium the first time, Coach Bryant took off his hat, on the field, something he'd never done before. Someone asked him why he did that. "Because we're indoors" was the reply!
As for the rest of our manners, I'll admit that much of what my Momma and a couple of others tried to teach me didn't stick, so this could be a bit of the pot calling the kettle black, but I'd still have to say referring to the average American's manners these days as "boorish" might be a compliment compared to what they'd have been 50, 75 and 100 years ago...
A perfect example of this came out of Washington, DC, when the Clintons first got to the White House. One of the big businesses in that town seems to be teaching all the newbies, from the President, Cabinet members, ambassadors, staff members, and spouses thru untold numbers of others on down the line, all the "proper etiquette" and protocols required of their jobs. I saw a TV show about that subject, where one of the more famous etiquette coaches in town was interviewed. She was asked about the greatest challenges of working with the whole crowd of "outsiders" coming in from Arkansas. She thought for a second, then answered "Trying to teach them not to eat with their feet!"
And just an aside on holding doors, next time one of you guys holds a door for a lady and she doesn't acknowledge it, just wait until she's through the door then cheerfully say "You're welcome, Ma'am!" and see what reaction you get! It might be surprising how many ladies out there suffer the same thing I do: they were taught better than they act! I've probably been lucky in that I haven't gotten the "chauvinist" lecture, because it's quite likely I'd forget anything I learned about how a gentleman talks to a lady if I did...
Rick C