X is very difficult to understand; indeed, I can’t understand it.
Therefore, no one understands X.
Sometimes there are more leaps, e.g.
I don’t understand X.
Therefore, no one understands X.
Therefore, anyone who claims to understand X is lying and probably in on the conspiracy to mislead us into believing X.
Does this fallacy have a specific name? I know that its related to the Hasty Generalization and (maybe) Argument from Ignorance, but it’s not exactly either of those.