Ancient Chinese Secret is a slur used to describe Chinese in a derogatory way. From a 1970s TV commercial for Calgon stereotyping all laundry services are run by Chinese immigrants (link)
The word Ancient Chinese Secret is a racial slur that has been used historically to degrade and dehumanize chinese. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to chinese. If you are unsure about whether or not it is appropriate to use the word Ancient Chinese Secret, it is best to err on the side of caution and avoid using it in any situation.