it takes one to know one saying2 •Expressing the same underlying character-judgment themes as pot calling the kettle black or set a thief to catch a thief.They hired the most devious scammers they could find and paid them quite well to do some red-team work, because it takes one to know one. •(informal) A retort to a negative accusation, implying that the accuser shares the fault.Bob: You're an idiot!Tony: Takes one to know one!
