So, imagine you have a piggy bank where you put all your money in. One day, someone you don't know comes and asks to borrow some money from you. You don't know if they can pay you back, but you give them the money anyway because you want to be nice.
But then, that person uses all your money to do something really risky like gambling or buying something they don't need. And they lose all the money! Now, they can't pay you back because they don't have any money left.
That's kind of what happened in Ireland in 2008. The Irish banks lent a lot of money to people and businesses to buy houses and start companies. But some of these people and businesses couldn't pay back the money because they had taken too many risks and they lost everything. So, the banks lost a lot of money and couldn't pay their own bills and people who had saved their money in the banks couldn't get it back.
The government had to step in and help the banks because if they didn't, the banks would have gone bankrupt and that would have hurt a lot of people who relied on them. But helping the banks cost a lot of money and the Irish government had to borrow money from other countries to pay for it. That made things worse because now the government had a lot of debt too.
So, the post-2008 Irish banking crisis was a big problem because the banks took too many risks and lost a lot of money which made it hard for people to get their own money back. The government had to help, but it cost a lot of money and made things harder for Ireland in the long run.