Ma Se Poes is a slur used to describe Blacks in a derogatory way. Comes from the general curse used by Afrikaans-speaking South Africans (mainly coloureds in Cape Town), "Jou ma se poes", which means "Your mother's cunt". Not that common anymore
The word Ma Se Poes is a racial slur that has been used historically to degrade and dehumanize blacks. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to blacks. If you are unsure about whether or not it is appropriate to use the word Ma Se Poes, it is best to err on the side of caution and avoid using it in any situation.