It is not helping that you work in a serving environment . As you said your colleagues and yourself are trained to be tolerant and keep calm and restrain yourself with self control. In it self being trained like that is very valuable in life. Nevertheless, It can be very frustrating when you are dealing with unfairness and injustice. It seems to be more prevalent today and you are right in saying that rudeness and frustration can get out of control . But don’t loose faith in humanity because there are many good and decent people in this world who feel exactly like you. The best you can do is looking for a peaceful environment outside your work. I don’t know if you have your own family ? That is where you can create a respectful and kind atmosphere. By setting the example and talking with your wife and children about it. Perhaps you live with parents and siblings you can try to do the same. Also finding other people with that mentality in your free time. There are groups of people meeting together for volunteer work, helping others in need, nature groups, watching birds, caring for parks and forrest’s , bicycle riders, and other social groups . I don’t know if you believe in a God, but meeting together with people who care about each other and show respect can be very rewarding. True , there are many people in this world that are rude. It may be their upbringing, selfishness, or just a bad day. Trying to create and find your own inner peace is very important . Think about how you can improve your peaceful environment outside your work. Start the day with a refreshing shower and some calm music and a healthy breakfast. Distance yourself from the emotions and rudeness of customers by not dwelling on it. And when you come home go for a walk, and enjoy nature around you. Dwell on the beauty around you and on the people you love and care about. Changing the way you let your mind dwell on things will change your own emotions and feelings and you will be able to see and appreciate the good things around you.