From Longman Dictionary of Contemporary Englisha chink in somebody’s armoura chink in somebody’s armourFAULT/something WRONGa weakness in someone’s character or in something they have said, that you can use to attack them → chink
Examples from the Corpus
a chink in somebody’s armour• Perhaps spotting a chink in Clinton's armour, the Republicans have further accused him of stirring up feeling against the war.• Perhaps there was a chink in the Tuer armour?• The film-makers used a chink in the technological armour to record the candidates in their unguarded, uncensored private moments. 