脱裤子放屁 (tuō kùzi fàng pì)

Literally: Taking off your pants to fart

Example: “邮件已经发了，还要打印出来再寄一份，真是脱裤子放屁。” — The email's already sent, and you want to print and post a copy too? That's pointless busywork.

Origin: A xiehouyu — a distinctive two-part Chinese folk expression in which the first half sets up a vivid, often comic image and the second half delivers the actual point, frequently left unsaid because the intended audience already knows how it ends. In its full traditional form, the saying runs "脱裤子放屁——多此一举": taking your pants off before passing gas — completely unnecessary, since it accomplishes nothing a fully clothed person couldn't manage just as easily. The saying is traced to the Ming-dynasty story collection Xihu Erji by Zhou Qingyuan, and later appears in the modern writer Lao She's work Can Wu (Lingering Fog) as well, showing centuries of continuous use for exactly the same idea: going through an elaborate, entirely pointless extra step to accomplish something that needed no such step at all.