A rod/stick to beat somebody with - Idioms by The Free Dictionary
a rod/stick to beat somebody with
stick to beat (someone or something) with
Something, often a mishap or misdeed, that is used as an excuse for criticism. Even the slightest mistake by Stan was enough to give the boss a stick to beat him with.
a rod/stick to ˈbeat somebody with a fact, an argument, etc. that is used in order to blame or punish somebody: The results of the national exams this year are being used as another stick to beat teachers with.