Hey the major problem with you is that you unusually think too much and think about every minute details. First you don't need to take life that much seriously. And fir this you need to keep your mind free and keep it calm.. now the question is how can you achieve that..?? The one way of achieving is by meditation and by exercise.. initially you find it very tough to do that but later you yourself start seeing the progress..
No coming to the second part of your questions..how you need to react in situations of disrespect and disregard. For this I would say do what your heart say. And don't keep your grudge over small things and every other person. You can only control your behaviour and you do what you think the right thing to do(assuming yourself as the receiving end).. revenge or giving befitting reply will never allow your mind to stay in peace. But ignoring do keeps you in peace...