Whats the point...

Would someone please enlighten me on the purpose of St. Patricks day? Becase so far the only things I have come up with are that it is an excuse to inflict physical pain on people, to get drunk, and to throw a beer can at the side of my nice car (which I am still really mad about!!!) all while wearing the color green! oh well thursday I will be in Las Vegas and I CAN'T WAIT!! but if someone could tell me why we celebrate this day please let me know!