This isn't true, not sure what you're basing this on. Britain and Ireland have had a troubled relationship since the late 12th century (we're all cool now), but beyond that I'm not aware of any other 'animosity' with any other nations. The Irish were broadly well received wherever they have emigrated to.

We also got on very well with Spain

In 1680 King Charles II of Spain issued a decree stating that 'the Irish in Spain have always enjoyed the same privileges as Spaniards. This has always been the practice and is actually so today.'[12] King Philip V of Spain issued decrees in 1701 and 1718 confirming these rights, stating that the Irish were to be treated as native Spaniards.

Ireland has had a long history of emigration particularly to North America and Great Britain. During the great famine of 1845-1852 at least 1 million people emigrated, and this event had enormous impact both politically and socio-economically - emigration continued steadily after the famine, so that by the turn of the 20th century the population of Ireland had more than halved from pre-famine levels (approx 1 million died during the famine period also).

Apologies if this is not up to the standard of an AskHistorians top level comment - but to answer your question why so much animosity, this is more of an opinion but I would suggest that the large influx of extremely poor Irish immigrants over a sustained period of time may have contributed to the animosity felt in the host countries towards the Irish.