fighting over nothing; making a mountain out of a molehill
A classical Chinese-derived idiom (故事成語) used to describe a trivial quarrel or a dispute over something insignificant. Rare in everyday speech; mostly encountered in literary or formal contexts.
Their argument is just a storm in a teacup.
A synonymous classical idiom with the same meaning and origin, also rare.
From a story in the Chinese classic Zhuangzi, where two states on the horns of a snail fight over territory, symbolizing a pointless conflict over something tiny.