having two sharp edges for cutting

a two-edged sword 双刃剑

A two-edged remark can be understood in two very different ways, one of them positive and one of them negative.

"That was amazingly generous of you!" "Well, that was a two-edged comment - are you saying I'm usually mean?" “你这么慷慨，真令人吃惊！”“这话可有两层意思——你是说我通常很吝啬吗？”