play hard to get idiom
（尤指恋爱之初）故作冷淡；装出矜持之态
to pretend that you are less interested in someone than you really are as a way of making them more interested in you, especially at the start of a romantic relationship
Why won't you call him back? Are you playing hard to get? 你为什么不给他回电话？你是在故作矜持吗？