Have we as Americans forgotten all about manners?
My students have never heard of the "rule" that says that gentlemen remove caps when coming indoors. I have the ladies do so as well, since the caps they wear are not part of their "outfit" but are just like those the guys are now wearing--primarily, baseball caps. I didn't wear caps as a kid/teenager, so I had to wait until I got to West Point to be taught this rule explicitly. However, a meandering down the center of any mall will show that this behavior isn't taught anymore. Heck, how many people don't even remove their hats during the national anthem at a sporting event?
Then there's manners related to how you treat a guest. Here's an example of how not to behave.