This is a popular internet meme in Chinese culture. It originates from a comedic skit where a character boasts, "I have a forty-meter long blade, and I'm going to swing it at you!"
It's used online as a humorous exaggeration to express uncontrollable anger or the urge to lash out, but of course, no such blade exists. Here, Jing Shu is jokingly saying she almost lost her temper and "unsheathed" her imaginary forty-meter blade.
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I pluck this from my footnote on chapter: The Old Master's Birthday Auction, The Cube Queen's Apocalypse Feast, Volume 3: A Torrential Banquet