When you forget you're in chat and you're trying to go forward and you end up publicly embarrassing yourself.
hotguy77: ill give you 20 dollars if you give me the legendaryskin dragoon1922: nah you scaming foo
dumbass69420: ey yo dont scam
dumbass69420: wwwwwwwwwwwwwwwwwww
hotguy77: look at that idiot trying to move but forgot to get out of chat
(on weeaboo sites and chatrooms) to lol. The "w" comes from "warau" (笑う), Japaneseverb for "laugh". The actual number of w's used is immaterial but 5 is considered to be a common minimum.
Haruhi: Previews are worthless, listen to my song!
Kyon: BOMBERRRRR!!!
RandomWeeaboo: wwwwwwwwwww