The A4 Waist Challenge is a viral social media trend that first gained massive traction on Chinese platforms like Weibo in early 2016 before spreading globally. Participants hold a vertical sheet of A4 printer paper in front of their midsection to demonstrate that their waist width is equal to or less than the paper’s 21-centimeter width. While originally intended as a fitness milestone, the trend sparked significant controversy regarding unrealistic beauty standards and body image. In the meme world, it is frequently parodied by users who use A3 paper, hold the sheet horizontally, or replace the paper with humorous objects like pizza boxes to satirize the obsession with thinness.