Green is a slur used to describe Irish in a derogatory way. The Irish were once loosely called the green race.
The word Green is a racial slur that has been used historically to degrade and dehumanize irish. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to irish. If you are unsure about whether or not it is appropriate to use the word Green, it is best to err on the side of caution and avoid using it in any situation.