I don't really celebrate St. Patricks Day. It's a horrible holiday with religious oppression at it's core. Everyone's heard the legends. That St. Patrick drove the snakes from Ireland, but we're not talking about reptiles. Snakes were used by the Druids as their religious symbol, and thus "snakes" also became a derogatory term for the druids. So the holiday is less about reptiles, and more about forcibly bringing Christianity to Ireland.
Not concinced yet? Let's go a step further. What happens to you if you forget to wear green on St. Patty's day? You get pinched right? Oh this gets dark...
Think of the Irish flag... what do you see? three color bands: Orange, White, Green.
Green has for a long time been associated with the Catholic faith. Orange, the Protestants... White is the universal color of peace. Therefore the Irish flag is saying that there should be peace BETWEEN the Catholics and the Protestants.
So if Green is a Catholic color, and you're suppose to wear green on St. Patty's day (a Holiday for a Catholic saint), or else you get punished by getting pinched, basically what you are saying is you'll be punished for being a non conformist to the Catholic dogma.
Now you've been educated... let's have a beer!