That's "Happy St. Patrick's Day", for those few among you who may not be fluent in Irish Gaelic.
Indeed, this is the day of the year when Irish and faux-rish around the world get together and celebrate the Feast of St. Patrick by guzzling green beer and consuming foods that, any other day of the year, would be considered high crimes against cuisine.
All of this in order to celebrate St. Patrick, the saint noted for bringing Christianity to Ireland and supplanting the previously dominant pagan beliefs of the locals. Or, to use the colourful metaphor, he "drove the snakes out of Ireland".
Good thing, too... damned pagans and their drinking (whoops) and carrying-on, their observances of the passing of the seasons, and the cycle of the moon... they NEEDED to have their silly, superstitious ways corrected.
Incidentally (credit to daveberta), St. Patrick's Day was actually MOVED by the Vatican this year, due to a conflict with Holy Week (the week leading up to Easter).
You know... Easter. The celebration of the death and resurrection of Our Lord. Which has nothing at all to do with Ostara, the ancient pagan festival held in spring that, as a fertility rite, was signified by rabbits and eggs...
Well, at least we're over those silly pagan superstitions now.
Did you ever wonder why the date of Jesus' birth never changes (it's always December 25th), but the date of his death and resurrection change every year, sometimes varying by almost a month?
Easter, for future reference, is always the first Sunday following the first Full Moon after the Vernal Equinox.
Damned pagans. Good thing St. Paddy got rid of 'em.