While it's true that italians range from tanned with black hair to fair complexion with redhair, there are some common rules most people swear by.

Fashion rules:
It all comes down to this: never wear ugly shoes.

That's how I know I'm in a foreign country. Everyone who's not wearing common sneakers, is wearing ugly shoes. You can tell fake leather from afar.

If you're a male, never wear sandals or fake leather shoes. Shoes with strap laces are also off-limits. Superga are very italian sneakers, and they're cheap. Clarks desert boots are also an Italian staple since the Seventies. They're classy but not fancy, can be dressed up or down, they're comfortable.

If you're a female, never wear Crocs or flip-flops outside of swimming pools and beaches. You'd rather wear converse or non-branded leather shoes than fake ones. Kitten heels are off-limits, but you can rock ankle boots.

Food rules:
Never have cappuccino after 11am. Never. We jokingly say it's a "German" thing to do ;)

Never put Grana/Parmiggiano on your seafood pasta. Or fish. Or seafood. Not sure why, that's just the way grandma taught me.

Please, pretty please, remember that eating pasta never involves a spoon. Unless you're home alone and eating 200g of pasta with melted mozzarella and tomato sauce in a bowl, then it's okay but don't tell anyone.

Don't put mayo on your italian pizza. Or ketchup. Chili infused oil is acceptable.

--

These are the heuristics that seem to apply to most Italians. They're probably shared with countries that share a similar culture in Souther Europe. Like everyone else, we're cool but we're not entirely unique ;)