Lululemon has filed a lawsuit against Costco, accusing the retail giant of infringing on its patents by selling knockoff versions of popular athletic wear, including pants and hoodies. The lawsuit claims Costco is trading on Lululemon's brand reputation and "sweat equity" by using lookalike designs that mimic their original products. This legal action highlights ongoing concerns over intellectual property rights in the competitive athletic apparel market. The case underscores the importance of protecting innovative designs and brand identity.