"Hee hee" is a commonly used word in social tools to express happy and pleasant emotions.
In the popular internet language and emojis recently, "hehe" and "not hehe" often appear together, usually conveying a contrast and sense of comedy between happiness in one moment and bad in the next. It is somewhat similar to the previously popular "I cried, I pretended".
For example, the mood of a worker on Sunday may be like this: today off, hehe; tomorrow I have to go to work again, not hehe.