以其人之道还治其身

leave sb. to his own devices pay sb. back in his own coin catch sb. with his pants down (of an official) clean and devoted, and govern the state with his own example of uprightness physic give sb. his gruel make sb. open his eyes get sb. on his ear put sb. through his paces walk sb. off his legs put sb. in his place leave sb to his own devices pay sb back in his own coin leave sb. to his own devices pay sb. back in his own coin a dose of physic catch sb. with his pants down catch sb with his pants down his very own physic on sb's own showing by sb's own account