In my past experience... PHWonline. When I joined, I was almost shocked at how incredibly immature they were compared to every other forum I was a part of. These guys just threw themselves at me. Not to mention the corruption going on with the staff, which only made things worse. Apparently, the site owner was a dick.
The place has great Garry's Mod comics though. And I mean GREAT.
Currently, however, I'd have to say the WoW community (well, it's no longer a community as far as I'm concerned). I'd say 4chan, but that doesn't even count as a community to me.