With the passage of time, young people have given it a new definition, and different people use it in different ways, which can be roughly divided into the following usages:
Irony. Force a smile or fake a smile. Angry or annoying. When is irony? For example, you are showing off your happiness with a friend, but this friend is more insincere than you, so you think he and you are good friends. At this time, you are particularly happy, but he is not sincere. This expression may be jealousy, so his expression may be irony.
When you smile or fake smile with this expression, it is another situation. For example, you kindly helped your girlfriend. For example, if you tell your female friend that you paid for a fitness card for her, in fact, she will send this expression when she doesn't want to do it, which not only expresses her gratitude, but also expresses her helplessness.
When two people quarrel, they often use this expression. For example, others are angry and scold you. At this time, you deliberately want to make him more angry, so you make this expression, which will make others more angry and play an ironic role.