Many experts say that one of the reasons many of us are overwhelmed and over-stressed is because we just can’t bring ourselves to say 'no' to people. Imagine having to do it in a foreign language, Italian for example!
You might argue that this is probably the simplest Italian word because 'No' in Italian is 'no', exactly the same as in English.
However, that might not be enough. Maybe you do not want to say a harsh 'no' but you do not know how to be more polite and diplomatic in Italian. Maybe you have been told that Italians might get offended if you say 'no' to a list of things: yet another espresso coffee, more mamma's food, coming to visit you unannounced, etc.
Here are some options:
Just adding a 'thank you' makes your 'no' sound less harsh, so
No, grazie - No, thank you
La ringrazio, ma per questa volta è no - Thanks, but not this time
No, grazie, ma sarà per la prossima volta - No thanks, maybe some other time
Vorrei, ma non posso - I would like to, but I cannot
Less formal and not as polite, the following are phrases you would only say to a friend:
Non ci penso proprio!- No way!
Neanche per sogno! - Not even in your dreams!
Non mi va - I do not fancy it
Obviously, in Italy one of the most difficult moments is the one when you need to say 'no' to food. To your friends offering the second serving of the lasagna they made at home with so much love and care, to mamma's third portion of tiramisù, to nonna telling you 'mangia - mangia!'.
In this case you can say:
E' delizioso ma sono sazio/a - It is delicious but I am full
La prossima volta lascerò uno spazio per il bis - Next time I will leave some room for a second serving
Sono allergico a... - I am allergic to..
Sembra squisito, ma non mangio (ingredient), grazie - It looks delicious, but I do not eat (ingredient), thanks