It is NOT St. Patty's Day.

First.

If you absolutely must shorten the name of today's observance of the death of the Roman Catholic Saint Patrick, it is St. Paddy's Day. It is not St. Patty's Day.

Patty is widely used as the shortening of Patricia, or in reference to the circular piece of beef that you place inside a bun, while Paddy is short for Pádraig, the Irish name for Patrick.
—Lost in the Pond

Second.

Patrick was not Irish. He was Celtic/Roman, born in the 5th century in what would become known as Wales, abducted at early age as part of a slave trade, and taken to Hibernia, now known as Ireland.
—Thomas Cahill: How the Irish Saved Civilization

Third.

As one example of how the day is celebrated in the U.S., a Baltimore, Maryland, business association held its 'Irish' festival nine days before the actual observance of today's St. Patrick's Day. Pictured here were preparations for a Federal Hill Irish Stroll as seen in the South Baltimore neighborhood —or as the revisionists call it, Federal Hill— on 8 March 2014, outside the historic Cross Street Market.

There was little Irishness about the thing at all, in particular, the choice of beer: Miller Lite, Blue Moon, and Redd’s Apple Ale. As pallid in flavor as Guinness Stout has become —adulterated with flaked corn since the 1980s— at least it is an Irish-owned and Irish-made beer, and an internationally-appreciated beverage-icon of Ireland. These were things apparently unknown or unimportant to the festival's organizers.

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Considering today's expected augmented consumption of stout beer, this video from CraftBeer.com might be worth watching. It debunks some dark beer myths.

I've been using the toasted bread/dark beer calorie analogy for over 20 years now. Why didn't I secure a copyright?

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An alert reader noted, via Twitter, that Guinness itself isn't 'really' Irish, either, being since 1997, part of the British-based multinational alcoholic drinks producer Diageo. There are "plenty of Irish craft beers tho!", he added, although most of these, unfortunately, don't make it here to the U.S.