It's an old joke and I've probably told it before in these pages
Captain: We are about to land at Belfast Airport. For those of you adjusting your watches, put them back 300 years.
Today is 12th July, when Protestants in N.Ireland celebrate the Battle of the Boyne, a skirmish between a Dutch King of England and an Anglo-Scottish former King of England 322 years ago.
The modus operandi is for the Protestants to march past Catholic areas, taunting them, until the Catholics rush out and they all have a fight.
This year the Protestants say they have a secret plan to avoid casualties, but I can give them a better one: don't do it. Stay at home and behave like modern people.