涇渭分明 涇河水清，渭河水渾，涇河的水流入渭河時，清濁不混。比喻界限清楚或是非分明。
莠：狗尾草，很象谷子，常混在禾苗中。好人壞人都有，混雜在一起。
[grain or chaff;the good and the bad are intermingled; sheep and goats; there are bad as well as good people in the group; there are weeds among seedlings; thread and thrum] 莠:狗尾草,比喻品質壞的人。比喻好人壞人混在一起
無如眾生愚賢不等,也就如五谷良莠不齊?！濉?文康《兒女英雄傳》
指好人壞人都有，混雜在一起。莠，狗尾草。比喻壞人。《鏡花緣》第六八回：“此時臣國西宮之患雖除，無如族人甚眾，良莠不齊，每每心懷異志，禍起蕭墻?！?鄭觀應 《盛世危言·訓俗》：“至於海外貿易工作之商民，不下數(shù)千百萬，五方雜處，良莠不齊。”