拒受饋贈;白送的馬還看牙口;對禮物吹毛求疵
牛津電影裡 100%
to refuse or criticize sth that is given to you for nothing
My dear, never look a gift-horse in the mouth, particularly in this country.
釋義來自《牛津高階英漢雙解詞典》第 9 版