The term "ching" is derived from the Chinese word for "China," which is "Zhongguo." It has been used in Thailand for many years, and is not considered to be offensive in most contexts. However, there are some people who feel that it is an outdated and derogatory term, and prefer to use the term "Chinese" or "Chinese-Thai" instead.
Ching can also be seen as a reference to the Thai-Chinese community, which is a significant part of Thai society. This community has contributed much to Thai culture and economy, and many prominent Thais are of Chinese descent.
Despite its sometimes controversial nature, the term "ching" is still commonly used in Thailand and is not generally seen as offensive.