How to celebrate St. Patrick's Day in the United States: Cover yourself in green (bonus points for shamrocks), put a smiling leprechaun cut-out on your front door, head to your local "Irish Pub" after work, get rowdy and wasted.
How to celebrate St. Patrick's Day in England: Eh, maybe pop down to the local pub for a nice pint.
How to celebrate St. Patrick's Day in Ireland: Go to church.