What is Ireland hated for?
Maybe for breeding everywhere ? ^_^
More seriously, Irish are more victims than bullies, and the hate / anti-Irish sentiment has always be fueled by religious and political motives.
It's always easier to justify invading a territory when you say that their inhabitants are a bunch of incestuous wife-swapping savages than just regular folks trying to live in peace, with their own mix of culture and traditions.
The Normans were probably the first ones to do it, with the backing of the pope, back when Ireland was composed of multiple kingdoms under a High King. We were pagans who needed to be "civilized" after all.
After centuries of bullying and "holy missions", most of Ireland was effectively Catholic. So when the Great Britain decided that Protestantism was the way to go, we got another round of invaders willing to show us what Civilized means!
Of course I'm oversimplifying for the sake of brevity, but I think you can see the picture/pattern. Irish people have always been bullied by their neighbors, and the irony is that, by doing so, we have emigrated everywhere and a lot of the current population is at least "a bit Irish".
There is not much that Ireland can be hated for. Some British people hate Irish persons due to the IRA and the bombings that took place in the 70s and 80s. Other British people hate the fact that many Irish persons move to the UK to get jobs and/or to collect the dole. But since nearly half of Britons today have at least a little Irish in their blood, these are minority views.