While the number one rule of talking smack about someone may be "don't let them hear you," several folks have managed to mess up exactly that, leaving the subject of their harsh words to hear all the dirty — and heartbreaking — details of their not-so-nice conversations.

From the exact moment a child learned their friends were far from actually being their real friends to the disheartening confessions of a new boss and a husband's discovery of one very brutal message, here, are 21 of the most heartbreaking things people have overheard others say.