PHRASE
害人反害己；自食其果
If someone who has planned to harm someone else is hoist with their own petard or hoist by their own petard, their plan in fact results in harm to themselves.
例句
The students were hoist by their own petards, however, as Granada decided to transmit the programme anyway.
不过，学生们聪明反被聪明误，格拉纳达最终还是决定要转播这个节目。