That commercial jingle is such an earworm that it keeps playing on loop in my head all day.

earworm 是由 ear（耳朵）和 worm（蠕虫）组成的复合词，字面意思是"耳朵里的虫子"。这个形象的比喻用来形容那些像虫子钻进耳朵一样挥之不去的旋律，也就是我们常说的"洗脑神曲"或"魔性旋律"。