Is there any explanation for the "ojou-sama warai"?

[Guido]

This is the type of laugh that either often or unusually is heard from some female characters in anime.

A laugh that sounds artificial and accompanied by an "Ohohohohoho" sound.

The most recent example of this type of laugh I heard from was from Karin episode 15.

When Elda Maaka and Karera Maaka (Mother-in-law and Daughter-in-law) were glaring at each other scornfully and start making the "Ohohohoho" sound.

And there have been pretty much examples like:
Rukya from Hanaukyo Maid Tai
Naga from Slayers
Miu from DearS
Suisei-seki from Rozen Maiden Traümend

among few others.

[YoshiZumi]

I'm not exactly sure, but they put that laugh in to portray characters that were brought up well, being rich or being full of themselves. My idea works for most of the characters you mentioned. Karera is full of herself, Miu believes she was brought as the perfect DearS and if I remember correctly, Rukya from Hanaukyo was filthy rich.

[Dragnfly@Gamefaqs]

What's sad is I know a girl in real life who laughs like that and she doesn't watch anime.

Yeah, it's generally a "laugh of pride" as it's often called. Usually accompanied with something (hand, fan, etc) slightly covering the face. It's most common with rich girls and bossy housewive archetypes but doesn't always stop there.

It's also often followed by the other characters sweatdropping. If somebody corrects her or proves that her pride is misplaced then it usually shoes a close-up of her angry face accompanied by a "tch" soundclip.

[domino]

Heh, that laugh... the "hohohoho" with the pinky up that snobby rich girls do. I don't know its origins, but I'm going to guess that it was probably taken from an older shoujo manga (think Rose of Versailles). Such strange gestures seem to fit right in with old-fashioned shoujo...

And since a lot of these old shoujo characters looked fancy and wealthy and whatnot, they probably carried it on so that wealthy/fancy characters had the old-style shoujo laugh. I've seen manga where the art style will suddenly turn back into Rose of Versailles-style shoujo (a common gag) as they do the laugh.

[kj1980]

The earliest thing that I can recall from the top of my head is a famous novel called "Konjiki Yasha," written by Ozaki Kouyo that was written back in 1912. In it, a rich and spoiled girl laughs with "hohohoho" when mocking someone. Perhaps this might be the roots?

[Forbin]

Maybe because in America all evil villians laugh with the Ah Hahahahahaha type of sound and it evolved into the Hohohoho sound?

[Radiosity]

It always seems to be the really irritating snobby female who does that laugh. Sumire in Sakura Wars was guilty of that at one or two points, made me want to crawl into the monitor and slap her

[Guido]

I'm also aware that at least one of the characters in Maria-sama Ga Miteru also resorted with that laugh, though I cannot seem to recall which.

[froinlaven]

I'd say the ohohohoho laugh is no weirder than the American cartoon villain laugh. It's probably just an exaggerated invented sorta thing.

What weirds me out is the fufufufufu laugh. I think people actually do that in real life!

[lavielove]

Originally Posted by Radiosity

..made me want to crawl into the monitor and slap her

reverse action to "The Ring" indeed.

In "Itsudatte My Santa" , Mai laughs "hohohohoho" in almost every scenes .Cute but quite bossy.

[Paper Lilies]

Tomoyo-chan in CSS does that 'hohoho' laugh. Then again, she's rich. ^^