I can't bring myself to respond to someone called "intentional feeder". Yeah, I know, I screwed up his name. Report me ;P
As to the most toxicly played champ, I have got to weigh in:
It's going to be a carry, because they have the best chance at big kill counts (and that's totally all that matters, right), otherwise I would have guessed trolling Soraka. I also think it's got to be a traditionally mid champ, because trolls believe they are the center of the universe. Or LoL, at least.
So: Leblanc or Vlad.
</hopes he totally wins the response game>