1 The person is laughing so hard
The laughing crying emoji or the tears of joy emoji, as some people call it, is an emoji that means that the person is laughing so hard that they are now in tears.
2 It's not an expression of sadness
Some people get this emoji wrong and think that it's an expression of sadness, but the majority of people use it to indicate that they are happy and laughing hard.
3 It could refer to tears of joy
The emoji might also be used when something so good happened that the person was waiting for. In such a case, the person would mean that they are now crying tears of joy. (See What Is The Purpose Of The Yellow Heart Emoji On Snapchat?)
4 The joke appealed to them
Many people use this emoji to inform others indirectly that their jokes appealed to them. Because this emoji is considered more intense than a normal laughing face, it usually means that your sense of humor is appealing.
5 The person wants to end the conversation
Some people use emojis in order to end conversations. The laughing crying emojis is one of the emojis that are used by some people to mark the end of a conversation. (See What do people mean when they use the see no evil monkey emoji?)