Wiktionary
interj. (non-gloss definition: Parodying an ostentatious expression of evilness in online written forums, chat rooms.) n. A stereotypical laugh associated with villains in acting, sometime represented by "muahahaha."
Wikipedia
Evil Laugh is an 1986 American comedy horror film directed and starring Dominick Brascia, and co-starring Myles O'Brien, Jerold Pearson, and Kim McKamy. While the plot focuses on a group of medical students attacked by a masked killer while repairing a building over the weekend, the film touched on a tongue-in-cheek approach, with avid Fangoria reader Barney providing the voice of reason.
Usage examples of "evil laugh".
I heard his evil laugh echoing behind the helm, mocking me, and when he came near I saw the gleam of his eyes through the slit, staring at me as a wolf stares at a cornered rabbit.
Chaotica's evil laugh was cut off with a blast that seemed to light up the comet dust around them.
The spirit-wraith mocked the words with an evil laugh and came on wildly.