cryptoboss2020: over the last 6 months, cryptoboss2020 has posted an average of 4.8 posts of utter nonsense each day in a variety of forums.
OpenCryptoSystems: In just the last month, OpenCryptoSystems has made over 90 posts that rival those of cryptoboss2020.
Honorable Mention:Polo7: Polo7 hasn't been around since last November, but the brief appearance included some bold and ridiculous predictions that never panned out. I wonder if Polo7 is the same person as OpenCryptoSystems.
I'll give it to you: those two are definitely good candidates based on your criteria.
Man, I'm so bad remembering bitcointalk members' names--especially when they're shitposters, but I've always thought
Khristian (I hope I got his username right) was one of the worst, though I don't think he'd meet your criteria, OP, since he doesn't seem to be that active anymore. All of
his posts were generic nonsense, and they used to drive me up a wall. Sorry, I just had to mention him.