That's a good point there. I personally wouldn't be offended in any way by Irish flags, even ones with Celtic logos on them.
Banners supporting the IRA are definitely out of order though.
And the Spanish attitude towards British people really annoys me. Spain is still largely a poor country with much of their income coming from tourism. That's tourism from US travelling to them. If only we could collectively stop going there and see if they appreciate us once they're stuffed?