以子之矛， 攻子之盾

以子之矛， 攻子之盾 [yǐ zǐ zhī máo gōng zǐ zhī dùn]

1. ■ (What will happen) if you try to pierce your wonderful shield with your marvellous spear.; attack sb. by exploiting his weakness; beat sb. at his own weapon; pay a man back in his own coin; refute sb. with his own argument; set [use] your own spear against your own shield; turn sb.'s battery against himself; What if your spears were used against your own armour