"WTF Bomb" is a thing that's all over Youtube, it's basically a random clip that ends with another clip of a bomb (usually a big one) beeping before exploding while someone screams "what the fuck..." followed by an insane howl and a maniacal laugh.
The "WTF Bomb" itself originated from three things...
1. A Mega 64
parody of an interview with one of the guys who made the game "Cold Fear", where towards the end he goes totally crazy and does the howl and laugh while a bomb goes off.
The "WTF" part came from something else though...
2. An episode of the stop motion show "The Steve Moustache Show" where an action figure of wrestler Ted DiBiase gets a makeover and turns into a mutant. He freaks out, and one of the things he says is "what the fuck".
Finally, the beeping noise...
3. Most people say that it comes from Counter Strike: Source. I'm not sure, but it doesn't really matter.
So there you go.
Look up "WTF Bomb" on Youtube for examples. It's hard to put it into text.