Never been to Ireland, but from my driving experiences in England, when a little grey haired granny blasts by you in the roundabout, it is time to get with the program!
If it is one with 7 roads coming in and you can't see the one you want, just keep going around until you know your exit. My record was 2.5 times around.
When the roads get really narrow, get over as far as you can. Let the twigs hit the mirror. Slow down. The locals I'll blast by like nothing happened. They have been doing that since their early diving years. The only angst is when you meet a beer truck on the narrow roads. You always say to yourself, when does the beer truck come through here?
Just watch out for those twigs because right behind them are a lot of stone walls, as my brother-in-law found out...bye bye mirror. I joked that the rental car place must have a storeroom in the back stocked with hundreds of mirrors.
And on several occasions during the week, I had to remind him to go left in the roundabout, not right. I think my next trip will have to be to Germany...they drive on the correct side of the road.