Mardis Gras

Well for anyone who may not know Mardis Gras means Fat Tuesday, really. I know why people celebrate Mardi Gras, but I don't really understand the intense craziness just because Lent is coming. I mean why do a bunch of off the wall stuff and then fast for 40 days? Why not just choose to be "good" or "bad" year round? I like banana moon pies as much as anyone, but I would prefer to witness Carnival in Italy or Brazil than Mardis Gras in New Orleans (been there done that I was not impressed).