To mistake a person's good intentions for bad ones and turn against them; to fail to recognize someone's kindness. This is the first part of a two-part allegorical saying (xiehouyu), where the second part is [[不识好人心|不識好人心|bu4 shi2 hao3 ren2 xin1]].

a dog biting [[吕洞宾|呂洞賓|lu:3 dong4 bin1]]; to mistreat a person who is trying to help you or show you kindness