His apology sounded so weak and marshmallow-like, lacking any real conviction.

marshmallow-like 是由名词 marshmallow（棉花糖）加上后缀 -like（像...的）构成的形容词。marshmallow 是一种松软、甜腻的糖果，常用来形容事物缺乏实质内容或力度。marshmallow-like 在这里比喻"像棉花糖一样软绵绵的"，形容道歉显得空洞无力。