Revelers cheer on the marchers during the 251st annual St....

Revelers cheer on the marchers during the 251st annual St. Patrick's Day Parade in Manhattan. (March 17, 2012) Credit: Getty Images

Every year at St. Patrick's Day I get a lousy case of the guilts. This year's no exception.

It started last weekend when I marched with my youngest daughter and her elementary school in Mount Kisco's parade. There are lots of Irish families where I live, but no one would call us Little Dublin. The town is 35 percent Hispanic, according to the last Census count, with everyone else crammed into the remaining 65 percent. It's basically what Woodrow Wilson had in mind for the League of Nations, only a working version of it.

But when I got to the parade -- when one gets to any St. Patrick's Day parade in the United States -- everyone was dressed in something green, no matter their ethnic background. The man and daughter in front of us were from Africa. The family to my right was Ecuadorean -- the ones holding the Erin Go Bragh flags in front of the Israelis.

Gets me every time.

When I was kid I assumed people wore green on March 17 because Irish people are so nice. But ever since I was old enough to understand the definition of "ire," I've been checking and rechecking that math. And no matter how many times I look at it, it doesn't add up.

Because the truth is, we're not that nice.

Yes, we have that twinkle-in-the-eye thing going on. But beneath every twinkle lies a hair-trigger temper. The merrier we seem, the closer to snapping we are. Trust me. And that laughter? Masks deep genetic madness, in my humble Irish opinion.

As long as I'm stereotyping, I should add that Irish people are incredibly judgmental. If you disagree with us on something, we may never speak with you again. Ever. And that's among family. Irish grudges with non relatives can last a millennium. The idea isn't to waste the wrath like the Italians do with vendetta knives; the idea is to savor it, to twist and turn the thing like a string of pearls, because that's what grudges are to us.

What do you call an Irish person with a chip on both shoulders? Balanced, they say. I would add gainfully occupied.

Non-Irish folks routinely wave Irish flags at St. Patrick's Day parades, and that amazes me the most. Because as generous in spirit as I like to think I am, I can't see myself ever carrying another nation's colors. (I wouldn't even carry an Irish flag at a parade; I'd feel too disloyal to the Stars and Stripes.)

And that's really the root of my guilt. I feel bad because St. Patrick's Day forces me to acknowledge that there are lots of people in the world -- Africans, Asians, Greeks, Hondurans -- far more culturally magnanimous than I am. It kills me to admit it, but I'm not sure I'd dress for someone else's parade.

The Brits and Scots get it. You don't see them near St. Patrick's Day marches. They don't want to give the Irish the satisfaction, and that's fine with us because we've been nurturing gorgeous grudges with them for at least 1,000 years. My wife is half Scottish, and she wouldn't be caught dead in green between January and June. I think that's part of what attracted me to her, in some perverse and primordial way.

Justine DiGiglio in my office, a straight-talking 22-year-old Italian-American, informed me this week that celebrating St. Patrick's Day has nothing to do with liking the Irish. "It's just an excuse to get drunk," she said with characteristic candor. But I'm not willing to write off the sheer nicety of those green-clad Mexican and Guatemalan families lining the parade I marched in last Saturday.

I can't speak for all Irish-Americans on any of this. But I can say with confidence that the Irish, despite our faults, tend to have awfully good manners. And so on behalf of my fellow Irishman, I offer an emphatic thank you to all those of you who find yourself sporting a green scarf, hat or carnation this weekend. Thank you for the honor of celebrating St. Patrick's Day with us. We sincerely appreciate it -- from the bottom of our cold Irish hearts.

William F. B. O'Reilly is a Newsday columnist and a Republican political consultant.

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