forbidden fruit

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

禁果

something desired or pleasurable that is not allowed or is illicit

:
The secret affair was their forbidden fruit.
那段秘密戀情是他們的禁果
For some, staying up late feels like a kind of forbidden fruit.
對一些人來說,熬夜就像一種禁果