a tromentator is a mix between a commentator and a troll. Ideally he/she has the mindset of a troll, without the vulgarity and outright crassness. They occaisonally make salient and profound observations and contribute to the discussion, but make just enough to not get banned.
A tromentator in general will disagree with the majority participants on a thread.
a tromentator has yet to surface in our midst, but I'm sure some are out there.