A conflict or misunderstanding between people who should naturally be allies or on the same side; an internal dispute caused by not recognizing one another.
哎呀，这真是大水冲了龙王庙，一家人不认识一家人。原来你们俩是表兄弟啊！
Oh dear, this is truly 'the flood washes away the Dragon King's temple' – family members not recognizing each other. So, you two are cousins!
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