put up a union jack flag

Yobs might take it as a provocation.

Ireland?

good luck

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Why would anyone celebrate the jubilee in the Republic?

Then again we have numptys out celebrating Soviet victory day.

Why do you think it would be a not very bright idea/ an OK idea?

The colourblind Basques will be delighted anyway

Assuming the OP is not trolling and is indeed seriously thinking of putting up a Union Jack in their front window, I assume it would be because they are celebrating the jubilee of Queen Elizabeth II, Queen of the United Kingdom of Great Britain and Northern Ireland. She is not the Queen of England...

That said, Ireland is probably not the best country to stick what some would call a "butchers apron" in your front window. Many of your neighbours may just mutter under their breath about it, some may see the funny side that you would do such a thing, but some fools will take it upon themselves to mark you/your house as a target.

OP: If you are genuinely not trolling and don't understand why many here still have such strong feelings about this then you need to do some reading to understand why. Many brits come to Ireland completely ignorant of why there is this hostility, this is not their fault, its simply not a subject taught in most schools. You have been a member of boards for a long time so I doubt you're fresh off the boat so I'm guessing your trolling. Happy to be proved wrong :)

it's your decision whether to fly the Union Jack or not, with all the connotations that go with flying it in Ireland. Just don't be surprised when doing so inevitably provokes a violent reaction. Not saying whether that reaction is justified or not, just inevitable.