I use it as an opportunity to explain the signifigance of the struggle for religious freedom. It usually starts with"hey, why aren't you wearing green?"
I reply that I am not wearing green because I am a christian who believes in the freedom to worship God the way the scriptures teach. I then explain how the protestants were persecuted for their faith and the men who gather to defend their homes and families called themselves "orangemen" after the king Wm of Orange who was defending their rights.
I then make some kind of self-depricating joke about not asking simple question to history majors when they are drinking beer. Then they say something like "No, keep going this is interesting I have never heard about this before. I thought everyone wore green, you know because of St Patrick and all that."
Then I give a brief overview of St Pat's live and tell a few of the more dramatic stories from his life and then I start to talk about how the entire nation was changed at all levels, personal, families, culture etc as a result of the gospel. This gives an opportunity to ask "Did you ever wonder how something as simple as an Idea about a person (Jesus Christ) could change an entire country?"
At least that is my plan. I sometimes don't get all the way into it, and that is OK. I am not selling insurence here I am just trying to use an everyday occasion to get into the gospel.
BTW at the pub saturday night I was given a green t-shirt