Dink is a slur used to describe Vietnamese in a derogatory way. Used in the movies Apocalypse Now and Platoon to refer to the North Vietnamese. Comes from French Vietnamese "beaucoup dinky dau". Beaucoup means "very" in French, Dinky Dau is Vietnamese for crazy. Shortened, dink just means "crazy"
The word Dink is a racial slur that has been used historically to degrade and dehumanize vietnamese. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to vietnamese. If you are unsure about whether or not it is appropriate to use the word Dink, it is best to err on the side of caution and avoid using it in any situation.