Irish Americans are people descended from Irish immigrants to North America. Originally highly discriminated against by resident Americans. Though the initial discrimination has faded considerably over the past couple hundred years, many people native to the United Kingdom hold an intense bias against these people insisting they are not Irish, due to their being accustomed to the label not as a culture or ethnicity, but as a nationality.
It should be known that Irish Americans do not consider themselves to be Irish nationals, but instead as descendants from the natives of Ireland, most of whom are known to have emigrated from Ireland during the Great Potato Famines.
Those living in the United Kingdom, and at times Ireland, tend to react dismissively of these people's acceptance of their heritage.
In some way, this is a form of racism against the group, in an attempt to deny them their cultural and ethnic origins (let's face it, Irish ancestry is still a form of racial ancestry, and anyone who would be as quick to deny it ought be equally willing to deny the ancestry of anyone from any other national ancestry).
Though many neglect the history of their people and attest to their heritage out of ignorance there are many who maintain an informed perspective of their history as a people. It is unfortunate, however, that people react so negatively to the acceptance of a cultural origin.
"I'm Irish American."
"You you aren't, you git, you're just American."
"And Americans are a mismatch of different ethnic and cultural origins culminating in the form of not one culture, but many, among which are Irish Americans."