If nation-rps count, I once played as a brutal Absolute Monarchy dedicated to holding power at all costs even as the world modernized and left the age of Feudalism. This again is pretty small time as my fellows considered the nation I created to be more grey than anything, except for this one weird dude. I'll get back to him later, anyway my Empire turned on it's allies who held a important strategic resource. Fucking them over, and leaving them to the mercies of the oddballs... 'Utopia.' And then I consolidated my victory and ethically cleansed a pack of savages who were harassing my colonies. 

Sounds brutal eh? But get this, I was far from the worst. The worst was this weird guy's 'utopia,' which he described as a 'militaristic libertarian' republic. Sounds odd but I'll roll with it, but then it got really weird. You see; everyone was under constant surveillance by these weird mechanical 'eyes' who sought out unhappy people. And 'unhappy' seemingly solely belonged to the eye of the beholder as the Fedora considered anyone who was displeased with what he defined as 'progress' to be mentally ill and sought them out and sent them to 'hospitals' where they were 'fixed'. I won't go into detail lest this turn into yet another political flamewar, but the 'utopia' reminded me less of Arcadia and more of a grotesque cross between 1984 and a Brave New World.

All that, and he was a pretentious jerkass. And that was the worst antagonist I've faced so far.

I won't go into details, but thankfully the dork left in anger after everyone gained up on him and crushed his nation. After that; the RP was less of a chore, and much more enjoyable.