JUST THE JACKET AND TIE.
Take it from Irish legend, Bono, St Patrick's Day parties are better in a suit. Sure, you could show up in that same green t-shirt you puked all over last year, but you're better then that. So, before you wake up, slam a bottle of Jameson and start river dancing to the nearest drunken bag piper, dress yourself up a bit. Otherwise you may never find out where the gold at.