I understand that there are set phrases it can be used in (as mentioned in my first question about “non mais”) but what cases would it be used most naturally?
« Non mais sérieux, c’est quoi ça ? »
« Non mais il est fou ! »
« Non mais pourquoi ? »
Are these natural? If not, what are some good ways to use it to emphasize what you’re saying and what do they mean? Is there an equivalent in English?