forbidden fruit

US /fɚˌbɪd.ən ˈfruːt/
UK /fɚˌbɪd.ən ˈfruːt/
"forbidden fruit" picture
1.

fruto proibido

something desired or pleasurable that is not allowed or is illicit

:
The secret affair was their forbidden fruit.
O caso secreto era o fruto proibido deles.
For some, staying up late feels like a kind of forbidden fruit.
Para alguns, ficar acordado até tarde parece um tipo de fruto proibido.