to take advantage of official post for personal revenge (idiom)
食肉寝皮
shí ròu qǐn pí
to eat sb's flesh and sleep on their hide (idiom) / to swear revenge on sb / implacable hatred / to have sb's guts for garters
以其人之道,还治其人之身
yǐ qí rén zhī dào , huán zhì qí rén zhī shēn
to use an opponent's own methods to obtain retribution (idiom, from Song dynasty neo-Confucianist Zhu Xi 朱熹[Zhu1 Xi1]) / to get revenge by playing sb back at his own game / to give sb a taste of his own medicine
秋后算帐
qiū hòu suàn zhàng
lit. settle accounts after the autumn harvest (idiom) / to wait until the time is ripe to settle accounts / to bide one's time for revenge