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.
那段秘密恋情是他们的禁果
For some, staying up late feels like a kind of forbidden fruit.
对一些人来说,熬夜就像一种禁果