I agree with Bemildred, I try to be a good person mainly to feel good about myself, and because I think it's the correct thing to do.
I used to work in a job where I was around "the public" a large part of every day. After 30yrs of that I have to say that in general I have a very low opinion of humans. I've become pretty cynical over the years. There are of course many good, kind and generous people out there, but they don't get the attention that the greedy, narrow-minded and ignorant ones do. The latter seem to call attention to themselves by their crappy behavior.
It just seems that more and more people are only interested in themselves and what they want--rampant narcissism! Because of that they just walk over anyone else in their paths, as they are more special than anyone else. They need to get where they're going, so don't get in their way or inconvenience them. Traffic laws don't apply to them. The sign that says no cell phones in this office doesn't apply to them. You know what I mean.
Of course I rant and curse at those people while I'm driving--last week the woman in the car next to me had her i-pad tablet sitting in front of her on the steering wheel! When she looked over at me, she must have thought *I* was nuts, yelling and waving my arm at her. Why do people think that's ok? I don't get it either.
But I just have to think that I won't drop my standards and act like "those people". I like to be nice to wait staff in a restaurant, treat them well, say thank you to them and give a good tip, and hope I made it pleasant for them to serve me. I don't want to treat them like a slave, or make them feel like they are somehow beneath me. This makes me feel good, and enjoy my experience more. Maybe that waiter/waitress won't notice or care, but I can feel like I tried to be nice and that's all I can do. If you are polite and people misinterpret it or ignore it, that's on them and not you.
When I was working I was good at my job and efficient, so I would get the work done quickly. Others did try to put more work on me, since I seemed to have 'spare time', and sometimes I would help out or sometimes I would make myself unavailable or find projects to take more time, so I could truthfully say "Sorry, I don't have time now" or "I have to finish this first". I guess you'll have to figure out how to keep people from taking advantage of your skills at your own expense.
If I hate rudeness, then I should try not to be rude myself. I think I have to live with myself, my behavior and that's really all I can do. I don't think it's all in your head at all, I think much of society today IS mean. I don't accept it and I DO rant and bitch about it to myself or at home or with friends. I don't think there is an answer other than staying true to your own standards. You can think that you ARE 'better' than THOSE people because you don't behave in mean, inconsiderate etc ways.
I think it's one of the good things about being an introvert/loner, that you can finally escape to your safe place, at home or where ever, and those people can't get to you. If you are aware that you need down time to decompress, be sure to give it to yourself. Alone time is your friend, lol!!
So, that's my .02++++cents