Youn is a slur used to describe Vietnamese in a derogatory way. Used by Cambodians. Youn was a tribe of Vietnamese descent that lived along the border between Vietnam and Cambodia. Cambodians did not trust them.
The word Youn 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 Youn, it is best to err on the side of caution and avoid using it in any situation.