Pot-Licker is a slur used to describe Irish in a derogatory way. During the potato famine, the would lick their pots clean to get every last morsel of food.
The word Pot-Licker 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 Pot-Licker, it is best to err on the side of caution and avoid using it in any situation.