瓜田不纳履，李下不正冠

Explanation: Analogy Bixian Yi. With the "melon no shoe in, Lee is not the whole under the crown." 　　Source: "Arts class together," volume IV of a lead San Guowei Cao "gentlemen line": "Anti-Weiran gentleman, not at the suspect room; melon no shoe in, Lee is not correct under the crown."