Generally used in a derogatry manner, to indicate that a player's complaint about an unfair aspect of the game is playing a game in which this sort of thing is par for the course.
Experienced and Seasoned Haloer: WTH. Welcome to Halo.
Girl: Hey be right back
Boy: Yeah sure
*girl walks away and guy eats all the cookies*
Boy: munch, munch
*girl walks back in*
Girl: WTH!!!!! YOU ATE ALL THE DAMN COOKIES.
Other sites are Facebook, Myspace and Bebo.
It basically means 'What the hell' and is mainly used by teenagers who do not wish to curse outright or think it is cooler to use an acronym.
It shows many different emotions, depending on what context it is placed in. It can show surprise, happiness, anger and confusion.
Girl: "I bought you a handbag, it's Gucci."
Mum: "I'm breaking up with your father."
Boyfriend: "I don't love you anymore."
Boy: "I love you."