1.
to nitpick; to split hairs; to find fault with trivial details
To obsessively point out minor, insignificant flaws or details. Used critically of someone who focuses on trivialities instead of the big picture.
Forms
重箱 (tiered lacquer box used for food) + の + 隅 (corner) + を + つつく (to poke). Literally "to poke at the corners of a tiered box" — picking at the tiny bits of food stuck in the corners.
Also seen as 重箱の隅をほじくる (using ほじくる "to dig out" instead of つつく).
Usage
Almost always used critically. The phrase 重箱の隅をつつくような is a common modifier for words like 指摘 (criticism), 質問 (question), or 議論 (argument).