I didn't know this until last year. So for 26 years I said St.Patty's Day, not St. Paddy's day. I discovered this because I am Facebook friends with a very intelligent girl that I went to college with. We were just acquaintances, but she was super smart (and now she's a history professor). She had something about "St. Paddy's Day" in her Facebook status and I thought, "What an idiot! I can't believe she spelled it that way!" Well, I did some Googling and it turns out I'm the idiot! Did you know it's actually "St. Paddy's Day"??