chink in someone's armor
US /tʃɪŋk ɪn ˈsʌmwʌnz ˈɑːmər/
UK /tʃɪŋk ɪn ˈsʌmwʌnz ˈɑːmər/

1.
弱点, 欠点
a weakness or vulnerability in someone or something that is otherwise strong or well-protected
:
•
The prosecutor found a chink in the defendant's armor during cross-examination.
検察官は反対尋問中に被告の弱点を見つけた。
•
Despite his confident exterior, there was a chink in his armor when it came to public speaking.
自信に満ちた外見にもかかわらず、人前で話すことに関しては彼の弱点があった。