I will try to give my list of somewhat history and concise summary of what happened to China since 1920s and how it made China's tourist receive such terrible reputation.
1) During the Chinese Culutral Revolution that began in 1966 Chairman Mao called for a mass revolution of not only culture and tradition, but also morals and principles. Intellectuals were put in "reforming" prisions. Books were burned, especially Lao Zi and Confucius. Children were encouraged and sometimes forced to report their own parents who disagreed with the government, who were intellectuals, who were hiding wealth from the government. Mao also standardized all salary, resulting in nation-wide unwillingness to work and compete because there is no reason and motivation to compete anymore. IMO Every single thing that Mao did destroyed China's thousand's of years of tradition, culture, history, and values.
2) Since the Glorious Revolution, China suffered immense proverty due to rationing, lack of innovation, and lack of a competitive market. Mao encouraged people to grow farms and food and then in return take away the food and ration it. During the Revolution there were numerous droughts and famine and an estimated 30 million or more died. People were eating bark from trees, grass, dirt, sawdust just to fill their stomach.
3) When you grow up in such a impoverished environment you become very selfish and disregard other people's values and perspective of you. But the problem is, it wasn't just one generation of children growing up during the Revolution and Famine, it was 2, 3 generations living under it. This caused all principles to be abandoned. Parents teach their children how to survive, when you have to survive you don't care about anyone.
4) After Mao's Death and the advent of Deng Xiao Ping, things changed. Deng opened up China's market, allowed some more freedom, allowed political and reforming prisoners to leave, encouraged intellectuals to study. Many historians and Hong Kongers regard Chairman Deng as the most important changing force that led to China raise to superpower during the 21st century as he led China's economic reform. During Deng's era, China saw an large growth in economics and production.
5) After Deng, China's economics sped forward like a stallion. Though still communism, each Chairman continued to reform China's infrastruction, economic ties, and technological advancement. Most would say that this is currently China's Economic Golden Age. People became wealthy really quickly. There were many investments into textiles, metal, technology. But a such rapid economic and industrial growth had a down-side: the government and regulations simply couldn't keep up, hence, all the polluted rivers and air, and pesticide, herbicide, toxic heavy metal poisoning. These things are all side effects of rapid growth. In addition, without ethics and principles, many factories begin to cheat people out of money buy creating fake baby powder, fake eggs. Many food in China are fake and is toxic buy can be produced at a cheap price. That is also a side-effect of growth, Corruption.
6) With all these economic growth. The Poor became rich really quickly. Not just rich, but WEALTHY. What happens when you have a massive about of poor people with nothing, no culture, little morals and ethics, and suddenly had an unlimited about of money? They splurged and hoarded daily necessities because they still have their mentality of survival, however, they didn't realize the whole environment has changed. They did everything on impulse to survive or simply because they never had such luxury. So they binge drink, binge eat, buying out all the expensive liquor. Honestly, it human instinct. if you never had anything, and suddenly you can have anything, Yea, most people would just go and try and buy all sorts of luxurious items.
7) This leads to my explaination why so many people do not like Chinese tourist. Because of Mainland Chinese's sudden bloom of economic wealth, they begin to travel to places like Francis, Hong Kong and enjoy the luxuries. But a main problem is they were never taught the proper etiquette of being wealthy. Unlike Poor areas of China, other countries that were well developed have civil codes, culture, etiqutte, which Mao has erased from most Chinese. So when mainland Chinese travel to act like total foreigners, and just try and buy expensive things, not understand its underlying history, culture, and meaning.
8) The mass influx of Chinese new blue bloods, also caused massive fluctuations in local markets. Mainland Chinese start hoarding and buying out luxuries such as vintage wines, dried albalone, shark fin, etc. Sometimes they even buyout baby powder and food because China's food is heavily polluted. This caused massive changes in local economies world-wide, suddenly there is a HUGE demand with no supply. What should originally be $80 HKD, became $180 HKD. What should be a luxury, dried albalone/ shark fin that middle-class can enjoy once or twice a year for $5,000/$10,000HKD (respectively) became $10,000/$28,000 HKD (respectively). You see what is happening - the residual effects of Mao's revolution can be seen today because people were not educated about ethics, principles, respect for other, etc. This is reflected on mainland CHinese's behaviors and reflected upon China's reputation across the world.
9) This are some of the most inherent societal problems that resulted in China's infamous tourism reputation. But it can all be changed with time and education.
10) Keep in mind, I only stated some factors that contributed to China's poor reputation and some of these factors are from my opinions and speculations through reading and observation. There are many other factors. It may seem I am critical on mainland Chinese because I am, at times, ashamed to call myself Chinese as I would have to associated myself with such reputation. Which is another reason why most people from Hong Kong calls themselves "Hong Kongers" and not "Chinese".
TlDR - Mao's Revolution transformed China and brought about the erasing and abandoning of almost all Chinese cutlural, morals, ethics, and values. Famine and poverty caused people to further abandon these civil codes and created a generation of surviver. Deng Xiao Peng came and brought about economic reform - CHina's economy and industry grew very rapidly; poor people became very rich. The poor who have been deprived of luxury suddenly had a taste, human instinct took over leading to relentless binging affect local economies and creating resentment. In addition to lack of education and lost of cultural heritage and values, Chinese acquired their infamous reputation as terrible tourist.