To be hoist with one's own petard; to have one's own scheme or malicious act backfire and harm oneself.
他本想设下圈套陷害竞争对手，没想到计谋被识破，反而让自己声誉扫地，真是反治其身。
He intended to set a trap for his competitor, but his scheme was uncovered, and he ended up ruining his own reputation instead. He was truly hoist with his own petard.
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