1) We are not a Nation of mafiosi, just a 0,01% of us is, no need to bring the label on every Italian. We're not even violent and hot-blooded, we like to argue loudly and this may mislead.
2) The stereotypical Italian as greasy, short, fat and not clean is completely untrue. In fact we are moreless as tall as most Southern Europe people, we are cleaner than most of them, and surely the percentage of fat people here is much lower than in the US.
3) We're not a whole Nation of Catholic fanatics, in fact Atheism here is very strong, especially amongst young people, and other religions are pretty common and accepted also. Sadly the laws still are inadequate to this change of the 100% of Catholicism there was in the 20's.
There are many more untrue ones, but one is completely true:
Our constant gesticulating: we truly do that all the time, and for us it's a common thing to have tired arms after a long conversation.