Mah pitom is a multi-purpose expression in Hebrew. Literally, “What suddenly”, mah pitom can be translated as “No way” or “Don’t be daft.”
If your teacher springs a pop quiz on the class, you might react with “Mah pitom, we’ve had no time to prepare!” If a surprise visitor asks if she is intruding, you could graciously reply, “Mah pitom, it is always a pleasure to see you.”
Pitom is a biblical term, which Abraham ibn Ezra links to peti, fool. As Nachmanides explains, something that hits you pitom did not occur to you to as a possibility beforehand; hence you are caught off guard, like a peti. Pitom’s partner word is petah. Isaiah (29:5) warns the residents of Jerusalem that their retribution will come “lefetah pitom”— suddenly, in an instant.
Israelis use pitom, l’fetah, and l’fetah pitom interchangeably to mean suddenly. The modern Hebrew for surprise (and small toys distributed at birthday parties), hafta’ah, derives from petah.
Mah pitom is a translation of vos plutzem, one of many Yiddish phrases that have so seamlessly entered Hebrew.