Today's Saint-Patrick's day (march 17th). It's a very nice occasion to celebrate by drinking much Guinness and sing traditional songs and drink more beer.
Unfortunately, some people try to give an familiar shorter name: "Patty". But Irish folks are getting angry when they hear that. They love Saint Patrick, and they prefer "Paddy". A lot.
If you're not sure, please visit Paddy, not Patty website.