The extensive use of detergents in modern life and industry has seriously impeded ecologically sustainable development. Facing this unresolved global challenge, we herein propose a CAW (coating at will) concept to endow virtually arbitrary surfaces with underwater superoleophobicity that supports the fast and easy removal of oily stains by mere use of water. The key selling point of this CAW concept is its ability to sustainably regenerate the coating throughout an infinite life cycle. The foundation of this concept is to make use of rapid amyloid-like aggregation of lysozyme (Lyz) conjugated with zwitterionic poly(sulfobetaine methacrylate) (pSBMA). The resultant phase-transitioned Lyz-pSBMA (PTL-pSBMA) could quickly prime versatile surfaces to afford a robust colourless ultrathin nanofilm on surfaces with high hydrophilicity. As a result, the hydrophilic PTL-pSBMA layer endows materials with excellent underwater superoleophobicity and provides outstanding detergent-free cleaning efficiency to remove oily stains (e.g., greater than 95% on silk surfaces and 99% on dishes). With excellent optical transparency, biocompatibility and negligible effects on wearing comfort, the PTL-pSBMA further showed extraordinary cost-effectiveness ($ 675/ton) and great savings on water and energy by 40%-50%. Overall, this work proposes an ingenious CAW design that breaks down the long-standing surfactant contamination barriers in the traditional detergent industry. Such surfactant-free water washing strategy holds great promise towards scale-up application to replace commercial detergents in the removal of common stains from fabrics and kitchenware surfaces, thereby greatly inhibiting the negative environmental pressures caused by surfactant emissions and providing a transformative response to ecosystems and water resource protection on Earth.