St. Patrick's Day is less than a week off (Baltimore's parade is tomorrow afternoon), and I'm going to go over this one more time. If you want to be on familiar terms with the saint who brought Christianity to Ireland, and I am by no means suggesting that you should, call him St. Paddy.
I heartily endorse the seniments of The Provisional Government Of St. Paddy, Not Patty in its address "to the People of the New World":
"Each and every year millions of Irish, Irish-ish and amateur alcoholics are needlessly distracted from their Holy Tradition of drinking themselves into a stupor in the name of Saint Patrick, a Roman Briton slave holding the dubious honour of bringing Christianity to an island that would use it as another convenient excuse to blatter the hell out of each other for centuries. ..."
The distraction: getting the saint's name wrong.
"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.
"There's not a sinner in Ireland that would call a Patrick, 'Patty'. It's insulting. It's really as simple as that."*
To use "St. Patty" is to display yourself as a "daft eejit." Daft eejits abound, as you already knew, on the Internet, where @paddynotpatty continues to find dogmatic and unsupported assertions that "St. Patty" is more aceptable than "St. Paddy."
You, dear reader, do not wish to be publicly branded a daft eejit. Now you know how to avoid that.
*The Provisional Government has some additional suggestions, among them that "Irish car bomb" is not a cute name for a drink and that no one with a shred of respect for the many dead would thoughtlessly order such a beverage. Guinness, Smithwick's, Jameson, Bushmills, and the many other reputable Irish beverages will do nicely to get you hammered.