You would be surprised at how often people have wonderful manners when that is what you expect and how rarely people do things that force you to conclude they are not polite.
A lot of people are simply polite, that creates a wonderful base. Then there are people who treat others as they are treated or who look to others for clues on how to behave, this group really can shine when treated well. These people are lovely and I choose to spend time with them because they treat me with respect when they are treated with respect.
There is another group that behaves beautifully but simply have a different set of etiquette expectations then I do, manners are culturally dependent. These people are also ladies and gentlemen because they are treating me respectfully but they have a different playbook. If we are going to spend time together we will enjoy each other a lot more if we address this issue and agree to explain anything that seems confusing, otherwise we might unintentionally create hurt feelings. This is the hypothesis I try first when I am treated in a manner that does not feel respectful. I like to ask them to explain why they did the confusing thing, if you ask a question like this be delicate, manners are a touchy subject. Something like “I notice you don’t seem to look people in the eye and I was wondering if there is a reason or if it just makes you uncomfortable” will often work well if someone just has a cultural difference.
There are those who do not know what to do, these people mean well but fumble through ignorance. They are still ladies and gentlemen, they just don’t know how to behave. Because they mean well these people can often make excellent friends. But you can’t correct their manners! Ladies do not tell anyone ,except for children that they are responsible for, how to behave. What you can do, if you really think someone means well but doesn't understand, is to make a respectful request. For example, a lady may not say "a gentleman would open the door for me when I have boxes". A lady may say "could you get the door? my hands are full". If someone does not know how to behave you simply take omissions in courtesy lightly. If the pleasure of their company does not overcome this flaw, distancing yourself is perfectly acceptable.
You are entitled to be treated by a lady, but a lady does not expect people to change for her sake. A lady takes people as they are and then decides how much contact she wishes to have with them based on how pleasant she finds their company. Polite people are often quite pleasant so a lady must often be choosy.
There is a group that is fortunately quite rare. These are people who are rude out of malice or because they personally dislike you. It sounds quite hard, but you must not take things these people say personally. If someone is acting to hurt you they are telling you they don't want to be a part of your life and not longer wish to enjoy your company. This could be direct rudeness (off-color remarks, crudeness, and the like) but it can also be hidden rudeness where someone is perfectly lovely to you but treats others with a lack of kindness, or perhaps gossips to you. Sometimes we can all be a little snide, but a person who is regularly full of everyone else's faults is not someone you want as a friend, I assure you that they are busy cataloging yours too.