“不三不四”，汉语成语，意思是不像这也不像那（neither one thing nor the other）。即不像样子，不伦不类。形容不正派或不像样子。可以翻译为“dubious/shady/unsavoury(characters)”。

例句：

她的朋友尽是些不三不四的人。

Her friends are all pretty unsavoury characters.

有些不三不四的人在酒吧周围游荡。

There were some really dubious characters hanging around the bar.