این اصطلاح بیشتر به شکلی که در پایینتر اومده، استفاده میشه، اما معنی جملۀ شما میشه:
او کلاً عادت داره که بیفکر حرف بزنه و باعث ناراحتی یا خجالت بقیه بشه.
یا
او مادرزادی عادت داره که بیفکر حرف بزنه و ...
شاید بتونیم اینجوری تعبیرش کنیم:
He is used to put his foot in his mouth since his birth.
15 put your foot in it especially British English ,
put your foot in your mouth especially American English to say something without thinking carefully, so that you embarrass or upset someone :
I’ve really put my foot in it this time. I didn’t realize that was her husband!