There are many scientific hypotheses on what makes villains laugh while doing evil stuff, so let's explore each one of them in order to get an understanding of our beloved villains and why their infinite wisdom even in small things most people don't even notice and good people can't even understand.
Oscar Wild
If you see the evil laughs from the view of Oscar Wild and the decadent movement, the reason behind it is to make contrast between tension and relief, for him it's like the contrast in the drawing, you can see that in his novel The Picture of Dorian Gray, where the paint reflect the character basically, the character of Dorian Gray in the novel is the written form of the painting, the appeal of the evil laugh and the evil act itself is inseparable, you can imagine the villainess as a paint in its written form. For example You can see Myca in The Crow as the cinematic form of the painting of The Apparition by Gustave Moreau, watering her character down is like erasing the painting from the canvas to "fix it".
Albert Camus
Now that would be interesting, in order to explain why villains laugh from Albert Camus perspective, I have to make up a story, because I find making a story would provide the best way to explain what I want to say.
Let's build a story about the character of Ping Lu who was played by actress Ping Bo from Striking Rescue for example..
Act 1
Ping Bo is stationed on a roof and start taking out a villain while trying to take out their target, then goes after another villain and mange to take down the four of them, then goes after her fifth target who doesn't same to be a villain, but she fails in achieving her goal.
Act 2
Flashback showing four villains including Ping Bo with the other 4 villains preparing for a mission and going after 5 different targets, but something went wrong and it turns out it was a trap, and all of them fail their mission, yet, Ping Bo find the day is starting over with her waking from sleep and getting a call to join the team all over again, and she fails again, over and over.
Act 3
After failing multiple attempts, one of the villains manged to achieve his target, she return back to life, except she's not in bed, she wakes up finding herself pushing a giant rock, and not only her, also her colleges around her, except the one who succeeded in their mission, yet the one who succeeded was crushed by the rock.
Now, she understand that for her to survive, she has to fail over and over again, she even provoke the hero, by taken hostages, causing chaos, even leave him clues to get the ultimate result, and while the hero trying to stop her, she laugh because she found happiness in the absurd and choose life, and choose rebellion over surrender.
In the story I used the relation between the teacher and the student as our villainess left clues to the hero, I also used The Myth of Sisyphus as the villainess trapped in a loop, and also her laughing is like What Albert Camus said "The struggle itself toward the heights is enough to fill a man's heart. One must imagine Sisyphus happy." And also used The virtue of selfishness, as her actions were very selfish.
