If you want to express absolute disbelief in Italian, an exclamation you simply cannot afford not to learn is Ma dai!
Oh, come on! / Seriously?
Ma is the word for but, whereas dai is a catch-all exclamation used when:
- encouraging someone to do something (Dai, forza! = Come on, you can do it!)
- trying to get someone to hurry up (Dai, sbrigati! = Come on, hurry up!)
- you feel that someone has said or done something wrong, foolish or unbelievable (Dai, perché fai così? = Oh come on, why are you behaving like that?)
It is in this final sense of the word that the expression Ma dai! is used.
Marco esce con Camilla. – Ma dai? Non ci credo!
Marco is dating Camilla. – Seriously? I don’t believe it!
If you are really having trouble believing what the other person is saying, or wish to communicate annoyance, you can elongate the a sound (daaaai).
Qualcuno ha avvistato un UFO a Torino! – Ma dai! Piantala di dire scemenze!
Somebody spotted a UFO in Turin! – Oh, come on! Stop saying silly things!
Non riesco a collegarmi. Mi sa che è caduta la linea. – Ma dai, di nuovo? Non è possibile!
I can’t log on. I think the connection is down. – Seriously, again? It’s not possible!