* Tiksi slaps bdreadz around a bit with a large trout.
I remember reading a study that people laugh more around other people. Anecdotally, I can definitely see this in myself. If I find something funny that isn't shared with other people, I might not outwardly laugh, and it would look like my lol, rofl, hahaha, etc isn't genuine, but with a group of people I'd probably be laughing out loud at the same thing. It might just be expressing the same emotion differently.
It's the literal sound of a chuckle/giggle/light laughter. So when you say it aloud, you need only laugh naturally.
To see it in action go to http://nicovideo.jp and pick pretty much any video. Start watching with comments on, they scroll over the video, and marvel at the trails of www(wwwwwwwwwww).