1. Milk in the morning
Thou shalt only drink cappuccino, caffé latte, latte macchiato or any milky form of coffee in the morning, and never after a meal. Italians cringe at the thought of all that hot milk hitting a full stomach. An American friend of mine who has lived in Rome for many years continues, knowingly, to break this rule. But she has learnt, at least, to apologise to the barman.
2. Keep in simple
Thou shalt not muck around with coffee. Requesting a mint frappuccino in Italy is like asking for a single malt whisky and lemonade with a swizzle stick in a Glasgow pub. There are but one or two regional exceptions to this rule that have met with the blessing of the general coffee synod. In Naples thou mayst order un caffè alla nocciola – a frothy espresso with hazelnut cream. In Milan thou can impress the locals by asking for un marocchino, a sort of upside-down cappuccino, served in a small glass which is first sprinkled with cocoa powder, then hit with a blob of frothed milk, then spiked with a shot of espresso.
3. Never say 'espresso'
Which reminds me, thou shalt not use the word espresso. This a technical term in Italian, not an everyday one. As espresso is the default setting and single the default dose, a single espresso is simply known as un caffè. And don't say "expresso", either.
4. Double trouble
Thou can order un caffè doppio (a double espresso) if thou likest, but be aware that this is not an Italian habit. Italians do drink a lot of coffee, but they do so in small, steady doses.
5. Say it loud
Thou shalt head confidently for the bar, call out thine order even if the barista has his back to you, and pay afterwards at the till.
6. Just the ticket
If it's an airport or station bar or a tourist place where the barista screams "ticket" at thee, thou shalt, if thou can bear the ignominy, pay before thou consumest.
7. Standing room only
Thou shalt not sit down unless thou hast a very good reason. Coffee is a pleasurable drug, but a drug nevertheless, and should be downed in one, standing. Would thou sit down at a pavement table to take thy daily Viagra?
8. Some like it hot
Thou shouldst expect thy coffee to arrive at a temperature at which it can be downed immediately as per the previous commandment. If thou preferest burning thy lips and tongue or blowing the froth off thy cappuccino in a vain attempt to cool it down thou shouldst ask for un caffè bollente.
9. The permitted drinks
Thou shall be allowed the following variations, and these only, from the Holy Trinity of caffè, cappuccino and caffé latte: caffè macchiato or latte macchiato – an espresso with a dash of milk or a hot milk with a dash of coffee (remember, mornings only); caffè corretto: the Italian builder's early morning pick-me-up, an espresso "corrected" with a slug of brandy or grappa; and caffè freddo or cappuccino freddo (iced espresso or cappuccino) – but beware, this usually comes pre-sugared. Thou mayst also ask for un caffè lungo or un caffè ristretto if thou desirest more or less water in thine espresso.
10. That is all
Anything else you may have heard is heresy.