Built from
红颜 (hóngyán, 'red face' = young beautiful woman) +
祸水 (huòshuǐ, 'disaster water' = source of calamity). Traditional historiography pinned dynastic collapses on women —
妲己 (Dájǐ) for the Shang,
褒姒 (Bāosì) for Western Zhou,
杨贵妃 (Yáng Guìfēi) for Tang. Modern usage is often ironic or critical of that framing.