Piratecat
Sesquipedalian
Incidentally, this theory first came up in my last campaign when (a) my campaign map had a huge area of grassy horselands marked on it that was turning out to be really really boring, and (b) I had just read a book about Genghis Khan. Hmm, mongols like grassy plains, right? Enter the Mang, horse-riding orcish archers who invaded from off the known map in numbers coming close to 400,000; the PCs were amongst the first to discover their scouting parties. The heroes never learned why the Mang had left their homeland, but they could have dealt with it if they'd wanted to; instead, they got the heck outta Dodge before the main army arrived.If you really, really love part of your campaign world (or if part of your world is boring), destroy it and make the heroes deal with the event or the aftermath. You won't run out of plot hooks for years.
And when I got bored with having a big chunk of continent taken up by orcish archers, because the PCs had out-leveled the threat? An archmage engineered a magical plague that wiped out every single orc it got near. That way I had several hundred thousand rotting dead orcs and a huge power vacuum... which was quickly filled by necromancers who rushed in to animate the corpses, creating a new kingdom of undead.
One important rule in DM rat-bastardy is to make sure your players have a hand in world-shaking events, even peripherally. In this case, the PCs had previously saved the life of the mage who engineered the anti-orc disease. Every time they ran across those undead they got to think "Hey, we're indirectly responsible!" That was fun.