I know plenty of well-mannered, polite people, in both my online and offline circles. Of course, people have differing ideas of what is polite or acceptable behaviour, so I can see how you might think that people "just have no manners". As others have alluded to in this thread, you have demonstrated that you are still grappling with basic online etiquette yourself - I hope that the indignation you may have experienced (which led you to make this thread) allows you to exercise good manners in the future.

It can be difficult to navigate what one thinks is a reasonable standard of behaviour (Expectations? Reality!), which I think mostly stems from a lack of restraint, communication, or expecting someone to be a mind-reader. However, some things just bug the trout out of me, like trying to hang out with someone who is engaging with their phone instead of being present; or simply not saying thank you when it is deserved. Small things can carry a lot of weight.

One way in which I am working on becoming more polite is to try to accept praise or compliments, instead of simply deflecting them. It is polite to me to be humble, but over the years I've taken it so far that I basically end up invalidating anyone who tries to say something nice about me.