Paddy Versus Patty (from Grammar Girl)
March 17 is St. Patrick’s Day—the day we celebrate the patron saint of Ireland, who lived around A.D. 400 and is said to have driven the snakes out of Ireland, which probably meant bad people rather than actual reptiles.
March 17 is supposedly the day St. Patrick died, so we’re celebrating his death, which seems a little grim to me, but I’ve rarely met a grim person on St. Patrick’s Day.
Each year, millions of people who aren’t Irish annoy the Irish by referring to St. Patrick’s Day as St. Patty’s Day. Patty is a woman’s nickname—short for Patricia—and not short for Patrick. For the record, the correct short form is St. Paddy’s Day.
According to the Provisional Government of Paddy, not Patty, the D’s in Paddy come from the Irish spelling, Pádraig. Visit their site to be chastised in a proper Irish manner.
– See more at: http://www.quickanddirtytips.com/education/grammar/paddy-versus-patty?
Fictionophile 
It is ‘Paddy.’ It’s also my son’s confirmation name. The Catholic Church pays homage to Saints’ Holidays and marks their day of death as part of the Holy Souls and Divine Mercy. I know it sounds complex, but these days are celebrated.
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