A brilliant and scathing book at Ireland by top comedy writer Colm Tobin.      In Ireland, navel-gazing has become a national sport. If our TV panel shows aren't repeatedly raking over scandals from the past, they are horrifying us with portents of doom, stoking up fear about all the horrors and misfortunes that are surely only around the corner.      In The Really, Really, Really Rough Guide to Ireland, comedian Colm Tobin unmasks the true essence of this mysterious mist-green land with its jagged teddy-bear outline, lurking guiltily to the Western edge of Europe. Are the Irish really the slick, upwardly-mobile, bright-young things of Europe with the skinny jeans and the unnecessary spectacles? Or are they the slack-jawed simpletons you see staring toothlessly out of postcards, patting their donkeys, patiently waiting for death?      Irishness means more than merely holding a passport with a harp on it. Some say you can hear Irishness in the lonesome lilt of uileann pipes. That you can smell it in the farts of a billion Guinness drinkers. Look hard enough and you can see it winking back at you from the shimmering, oily thighs of Michael Flatley. But what is it, really? It's safe to say that Ireland is no longer just a physical place. Who are the Irish people now and where are they going? And who in the name of sweet Jesus is going to pay for it all?"