Many pagans don't celebrate St. Patrick's Day because St. Pat christianized Ireland and quite frankly, we still resent it. "Driving the snakes out of Ireland" is the mytho-poetic term often used to refer to St. Patrick's sometimes forced conversion of the local pagans. Snakes were powerful Druid symbols of energy and spirit.
Some pagans call March 17th Snake Day instead. To celebrate paganism's survival and current revival despite Christianity's best efforts, they wear snake imagery to show that, by Goddess, St. Pat didn't get all of us! Serpentine jewelry, pins and t-shirts are popular choices on Snake Day.
Others call March 17th Irish Heritage Day, preferring to retain and celebrate all the good things about Ireland while not lionizing St. Patrick and Christianity. This is the route I like to go. Irish culture is rich, complex and gives so much to the world . . .
. . . including some light-hearted fun too.
Well, everyone, guess I'd better sign off now and go practice my bodhran! Erin go bragh!