What does “montarsi la testa” mean in Italian?

Montarsi la testa is the Italian way to say someone’s “let it go to their head.” The verb montare can mean to mount, assemble, or whip up (as with cream), so the image is of a head puffed up with self-importance. Si è montato la testa = “he’s gotten too big for his boots.” It’s the classic family put-down for someone whose small success has made them think too highly of themselves.

Italian builds a whole family of idioms on testa (“head”): perdere la testa (lose your head, fall hard for someone), avere la testa tra le nuvole (have your head in the clouds). Montarsi la testa is reflexive — you inflate your own head — and often arrives as gentle mockery from people close to you, the exact sting of relatives saying you’ve gotten above yourself after a bit of luck.