It's actually a bit more complicated than that, which just ties back into the genius creation of the character. If all he wanted was the world to suffer, there are much easier, more crass ways to go about it.
Suffering for the Joker (at least Heath Ledger's Joker) is simply a byproduct of something far more desirable for him: The ability to make and shape people in whatever image he desires through carefully designed, intricate plans. It's actually debatable whether the Joker in "The Dark Knight" is actually insane, given the level of the natural genius he displays on a regular basis. He's obsessed with undermining a social order he sees as a joke, a lie, and a cover for peoples' real intentions and feelings.
Personally, I don't think this kind of character would work terribly well in the Fallout world for the simple reason that the game world isn't geared to respond to the level of diabolical, insane genius you would need to become. NPC characters don't remember times when you put a bullet in their leg and then ran off, nor can you commit acts of wanton terrorism. Given the kind of lives people live every day in the Capital Wasteland, the worst you could do to them is either kill them or make them suffer a little more, but how much more could you really add to the plight of people living in an irradiated world where death, disease, and sacrifice are as common as breathing?. There's no social order to disrupt since every community it's basically its own little society.
That's a pretty good argument, thnx for the input, but as all games NPC's AI are of course limited to the point you cant be a "psychological terrorist" of course id customise my joker (as little as possible) to make it work in the fallout universe. doing things like simply placing mines everywhere in megaton, and not even watch the carnage, just go into the saloon, have a beer, and walk outside, drunk, seeing scorched earth , mutilated bodies and A LOT of blood, laughing, and going to bed for the night.
Sadly, the joker's "essence" of being is severely limited in the fallout universe, but that's why I started this thread, thnx for your input, you rly made me think on a whole new level about how to make this dude work