Why Villains Laugh

It's a staple of most genres, really. Villains have their Evil Laugh, which they use a little too often for any sort of sense-making, but having one is more or less required. As Dr. Horrible said, having a quality Evil Laugh is an important thing.

A lot of guys ignore the laugh, and that's about standards. I mean, if you're gonna get into the Evil League of Evil, you have to have a memorable laugh.

He's right, of course, from a literary/entertainment point of view, but it prompts the question: Why? Specifically, why do they need a laugh, and in what way is it nefarious? Aside from the obvious (and perhaps circular) reason that for a character to be memorable it needs memorable traits, it does seem odd that villains have such a jolly time.

Firstly, it's not always about humor. There are a lot of reasons people laugh, and sometimes it has little to do with funniness. This is more article seed than article proper, so I'll just say this: One big reason villains laugh so much is that the hero-types do the obvious, play into the villains' plans, and are generally irrational and self-impressed. Even when the result (and often, cause) is awful, the blind insistence on doing what obviously won't work sparks the sense of absurd, and laughter follows. It just may not be the laugh of merriment.

Yes, I've been laughing a lot, lately. Why do you ask?