A Japanese term for (often evil) laughter. It is often used in manga or manga-styled scenes in anime when someone is deviously plotting something. It is mostly humorous.
And then, I'll put a tack on his chair! Fufufu...
Manical laughter. Used in place of "Mwahahahahahaha" and "Bwahahahaha" and "Gwahahaha" and "Fwahahaha" and all those other "hahaha"s in an attempt to be original.
Also the laughter used by the ninjas in the Pokemon games.
"Fufufufufufufufufufu...I'm evil. >=D"
"You're not evil when you =D"
"No, see...the eyebrows fix it! >=D"
The eviliest laugh ever
I'm going to rape your cat Fu Fu Fu!