"Saint Patrick's Day? Grand.
Paddy's Day? Sure, dead-on.
St. Pat’s? Aye, if ye must.
St. Patty's? NO, ye goat!
Paddy is derived from the Irish, Pádraig, hence those mysterious, emerald double-Ds.
Patty is the diminutive of Patricia, or a burger, and just not something you call a fella".
(we celebrate Ireland's month and St Patrick's Day quoting the wonderful self-explanatory website > www.paddynotpatty.com