“不三不四”，漢語成語，意思是不像這也不像那（neither one thing nor the other）。即不像樣子，不倫不類。形容不正派或不像樣子。可以翻譯爲“dubious/shady/ unsavoury(characters)”。
例句：
她的朋友盡是些不三不四的人。
Her friends are all pretty unsavoury characters.
有些不三不四的人在酒吧周圍遊蕩。
There were some really dubious characters hanging around the bar.