React stressed if a waiter doesn't bring the bill to the table by himself, although you have already finished eating (in Italy this would be rude from the waiter). You must ask for the bill.
Order a cappuccino in the afternoon. This will at least immediately expose you as a tourist, Italians only drink milk coffee in the morning.
Ask for something like Pizza Hawaii, or ask for Parmesan with seafood pasta. Also eating spaghetti with fork AND spoon will reveal you as a beginner, cutting pasta as highly uncultivated.