Mick/Mic/Mc is a slur used to describe Irish in a derogatory way. Many Irish surnames begin with "Mc" or "Mac." Many Irish are also named after the famed Michael Collins, making Michael (Mick) a very common name. Not as derogatory as Paddy.
The word Mick/Mic/Mc 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 Mick/Mic/Mc, it is best to err on the side of caution and avoid using it in any situation.