Frankly nothing...I'm 1/2 Italian, 1/4 Swedish and 1/4 English. But in honor of the day I usually cook a corned beef and cabbage dinner..'cause we like it.
I grew up in a town in Northern NJ that had a predominately Italian heritage population (hard to believe right???). When I was a kid some kids told us to wear orange on St Patrick's day if we weren't Catholic. Jeez I was raised in the Unitarian Church...my parents weren't too cool with that idea so I didn't do it. I had nothing against the Irish Catholic kids. Hell, I was one of the few kids who wasn't Catholic, the last thing I wanted to do was stand out in elementary school... I usually wore something green.
In 1977 I actually went to the NY St Patrick's Day Parade in NY..primarily to get drunk..which I did and didn't have such a great time because some guy puked on the back of my coat while we were jammed into some pub on 47th Street. Frankly it was a pretty awful experience. I never went again.
Looking back on my younger days, this day was just an excuse to get wasted ...now its just an excuse to make a yummy pot of corned beef and cabbage.
So.. Irish or not.... Enjoy your day.