In reality, there is a very limited circle of people who's opinion is actually the only one that really matters - the people who love you for who you are - your family and close friends. You see, the problem is we spend considerable part of our time thinking what others think about us, whereas we very often ignore what people that really care about have to say. Aren't they who's opinion should really matter to us, for they are the only one who have our best interests in heart? It's better to be loved by a few important people than liked by everyone. Here, in Russia, they have a very good saying - "I am not a $100 bill to be liked by everyone."
Rules are being set by the stronger
Rules are everywhere - whether you are at work or at a restaurant. People judge you when you break them. Remember, for example, Sex and The City movie, where the four great friends went on a holiday together and Miranda... Well... Watch.
Someone once said that women's body hair was gross, and in every way possible imposed the idea. Today beauty industry makes huge money on someone's genius statement, and those who don't care whether they look like Chewbacca, get judged! See, even I disapprove of hair situation being neglected.
You need all the resistibility in the world to stand up for what you believe in, especially if you are a minority like Miranda in the episode above. You don't necessarily need to be direct and tell people everything on your mind straight out, though. Not caring what others think doesn't mean being bold trying to make others change their mind. Not caring means being confident enough to not prove anything to anyone, to be comfortable with keeping your opinion to yourself.
They don't care
For particular individuals it might be a shock, but none of us is a center of the Universe, so stop over-thinking. Most of them simply don't care!
I would most certainly be right if I said you have spent a lot of time at some point worrying you said something wrong, or you didn't look great enough, or you were uninformed on a certain subject etc. Truth is, they probably didn't even notice the things you were so worried about, or if they did, they forgot about it right away - most of the people are far too busy worrying themselves what others think about them.
Life is too short to waste it on something that is most likely only in your head. Be fearless. And surround yourself with confident and successful people who don't have time to judge you, who can be a great inspiration and influence instead.
They can't hurt you
Unless you let them. People may often be rude, especially the strangers you would never meet again. You could spend your whole life trying to make occasional people in your life like you - by spending hours on your appearance, working on the way you speak, walk, think and so on. You have to ask yourself though whether it is worth it. Because these are the passerby people that might make an unpleasant remark about you, but they would forget about it - and you - the moment they turn around. So should you! These people don't matter in your life - why should their opinion do?
Don't forget that you aren't the only one who gets judged all of the time - you judge others by your standards as well and as much as others do, don't you? Liberate yourself from the prejudice chains and you will be shocked at how insignificant public opinion becomes.
Spend more time alone with yourself
Concentrate on what's important to you. Spend more time doing what makes you happy. Set your priorities right. Ask yourself how much time on average you spend worrying what irrelevant people think about when you could spend it productively for yourself? Once you recognise your values, know for sure who you really are and what you are aiming for in life, what others think becomes less and less relevant. It's all in your hands, really. Just be yourself, it's the best person you can be.