This was the name given to blacks in England and in America. It comes from the theory that the two underclass races would eventually merge together and form one race.
'No Blacks, No Irish, No Dogs' - sign posted on many places of work, phasing out a bit before the mid-20th Century. Many Irish pubs have an old sign like this put up above the door for ironic amusement and historical interest. As if to say, 'This is the way things were.'
"No -- We don't hire any paddies or smoked Irish here, now get to movin'"
'Spick' comes from the derogatory name for the Irish - 'Mick'.
Irish and Hispanics are both dominantly catholic. In the 1900's when Irish immigrants had pretty much been well established, but still hated by many Americans, was also the time when many Hispanic immigrants made their entry into America. They ended up sharing Irish churches, schools and neighborhoods due to the catholic faith and moral values we had in common. When early Americans saw this, they began calling hispanics "spicks" (Like a spanish Mick) for hanging around them.
"Those two were made for each other - a Mick and a Spick bastard!"