This one and
UQMF are the only ones I'm at all active in.
I was active in the silly Super Mario Crossover forum at one time, but was banned as a result of (in my opinion) terrible moderation and misuse of power. I don't recall the specifics, but I recall I was a bit of an asshole in one thread (meaning I used a "facepalm" image because I felt someone said something stupid) and it somehow skyrocketed into a bit of a flame war and then an argument which an admin got involved in (it was an argument of semantics; I was inferring something from what the admin said and, not knowing of the word "infer", was trying to explain this with the word "imply"; the admin kept saying I was putting words in his mouth, i.e. strawmanning, while I was trying to explain for something like 2 pages that it was a misunderstanding). The thread ended when I responded to the admin right after he posted, preventing me from seeing his edit that said something along the lines of "don't respond to this thread any more, use PMs instead". His response was to close the thread and then order everyone to never mention it again, even in PMs. Naturally, I was outraged by this; requiring continuing an argument in PMs is perfectly reasonable, but to require dropping it, even at the level of PMs, because I made a mistake? Of course, he made the reasoning that because he made the edit to his post so fast, I
obviously must have seen it, so I was deliberately ignoring him. So I sent a PM, against his orders, where I continued the argument in question, then I told him that the only reason I had responded in the topic was because I hadn't seen the edit. I figured I was going to be banned, so I also shared my existing gripes with the admin; namely, that he had a trend of requiring everyone to shut up and accept what he said to end an argument even when the argument was relatively civil, including one time when he ended an argument about tool-assisted speedruns by claiming "it's a macro and not really a person" (anyone who has ever visited tasvideos.org knows that's a pile of shit; it may be acceptable for how it works underneath, but it says nothing about TASes are created). Basically, I called him a bad admin. And as I suspected, his response was to permaban me.
So that's the only forum I can't stand. I would tolerate 4chan more than a forum that has a bad, power-abusing admin.