Thais and other Asians
To be honest, Thais generally have negative views of many other Southeast Asians, especially Cambodians, Burmese, and often the northern hill-tribes. Laotians are viewed similarly as Isaan people: ultimately cultural and linguistic cousins of the Thais, but uncouth folks from the boondocks. Many expats from these ethnic groups in Thailand feel discriminated against by Thais. There are many individuals that would get along quite well with each other, but as a whole, these nationalities do not get along and keep to themselves. In fact, I've had Cambodians here tell me that Thais are racist and bigoted (at least to other SE Asians). The northern hill-tribes have not been treated well by the Thai government either.
Northeast Asians (Chinese, Koreans, Japanese, HK/Singaporeans), however, are treated well and highly regarded. China and Japan have had positive diplomatic ties with Thailand for centuries, and since they do not border Thailand, they don't compete directly for land and resources the way that Cambodia or Burma had for centuries. The Chinese have been by far the best assimilated group, and Thais feel a special kinship with them, as many Thais have Chinese ancestry. There was a short period in the 1900's during which the Chinese were vilified, but this has long since passed. Today, they are still the "Jews of Southeast Asia." Many top Thai businessmen and politicians today have direct Chinese patrilineal ancestry. Across central Thailand, it is very common to find shops with Chinese characters, as well as Chinese restaurants.
However, local Thais are not particularly fond of the large groups of Chinese tourists who do not bother to speak Thai, have crude manners (from the Thai perspective), and act like stereotypical "sleazy tourists." There are many recent Chinese immigrants who do settle down and eventually blend in quite well in Thai society though.
South Asians (Indians, Pakistanis, and others) are called "khaek," which means "guest people." They generally are viewed less favorably than the NE Asians, although many South Asians have also integrated quite into Thai society over the centuries. Much of Thai culture ultimately comes from India.
Thailand has an assimilationist policy in that it only recognizes one official ethnic group and one official language: Thai. Everyone born and raised in Thai society will be expected to be Thai, not take on separate non-Thai identities. Hence, the wide range of looks that present-day Thais have, which can range from light-skinned NE Asian to almost South Asian (Indian)-like.
Thais are highly nationalistic, and the country has a strong right-wing feel, quite unlike China's strong left-wing feel with a neo-capitalist twist. As the wealthiest and most powerful Southeast Asian country north of Malaysia and west of the Philippines, Thailand feels very superior to its weaker neighbors.
Etiquette and social class in Thai society
Thailand is a very hierarchical society, which is quite evident in their language and etiquette. This stands in stark contrast to China, which feels much more egalitarian and feels far less hierarchical than Thailand. Thais have very elaborate ways of using correct words and phrasings to talk to people of higher/lower social standings, older/younger people, and so on. China is much more simple in that language etiquette is pretty much binary -- informal vs. formal (as with Spanish) for basic pronouns, such as "you." But in Thai, you would have a "proper" Sanskrit-derived term for words as basic as "eat," which would be used in formal contexts instead of the informal, "regular" native Thai term.
As a result, Thais are very deferential, very polite, and highly conscious of social class and status. In this respect, Thais are far more like Japanese than Chinese. Simple everyday purchases at convenience stores and restaurants all involve deferential head ducks and wais. Bills are often presented to customers with both hands. Thais also speak very softly (except for the hustlers targeting foreign tourists), much more so than the mainland Chinese. In China, people are much, much rougher, as the Cultural Revolution has made China a complete polar opposite of Thailand in many ways.
However, the down side is that oftentimes when Thais don't like you, they'll keep on being polite and won't say anything. The Chinese would tend to show immediate irritation when not impressed, on the other hand.
Beggars are treated much better in Thailand than in China. Thais have much more compassion than many NE Asians do with the less fortunate. In Thailand, it's actually good karma to give alms to the poor, whereas people in China just don't think this way.
People do line up in Thailand. Once in a while, a few impatient individuals may try to cut the queue, but this is surprisingly rare. Not so in China! Thais rarely spit too.
The Thais also take cleanliness far more seriously than the mainland Chinese and Indians do. People rarely throw trash willy-nilly as they do in China, and usually only drop plastic wrappings by the edges of sidewalks, not entire bags of food straight out in the open as in China. Streets are swept regularly, and homes are usually kept very tidy.
Thai bureaucrats and academics also do not cooperate well with each other, and form cliques within their respective institutions that can make negotiations difficult. Why? The short answer is that Thais do not trust each other very much. Comparatively, doing business and coordinating institutions in China would be much easier.
Thais will highly respect you if you dress like a proper middle-class, well-educated citizen, and if they know you went to a respectable university or have a respectable job. Sleazy tourists are not looked well upon by the educated class.
Just my 2 cents, please feel free to comment, ask questions, or object.
I'm not like the other expats who've lived here for a few years and still hardly know, or experience, anything beyond the foreigner enclaves.