What are the differences between Roman Catholic and Irish Catholic? I've heard the terms Roman Catholic and Irish Catholic since I was little, but I have never understood what, if any, are the differences between the two.  Why the differentiation of the two?  What makes them seperate?  How did they come to be seperate?
Irish Catholic is just a cultural distinction.  

There is an Anglican Church of Ireland which might consider itself truly Irish-Catholic in the sense that on England they'd call themselves Anglo-Catholic. But, that's not what people mean when they say Irish Catholic, they mean Roman Catholic or as Catholics prefer to say, Catholic. 

There are other countries/regions where having Catholic after the name is actually indicative of being another Rite of the church.  Assyrian Catholic, Ethiopian Catholic etc... They are still in communion (subscribing to the same teachings) with the Church in Rome. 

American Catholic, on the other hand, is a schismatic group that is not in communion with the Church in Rome.