Italy should of stayed neutral.

Why? So that way it can spend the time to invest in its military while watching and learning what each side is doing.

Once the war ends in the same way and Austria Hungary collapses while everyone is war-fatigue. Italy would be ready to invade the new lands that broke off of Austria-Hungary and take whatever they wanted. No one would've been in the position to stop them other than maybe the US which wasn't ready to enter a new war.