There's !justpost@lemmy.world, but there's another one that gets downvoted all the time where it's just one person saying violent stuff about their day in a community they moderate. Dude built the perfect rage room, and I can't remember what it's called.
Here is probably good.
Yeah, because no one reads the goddamn community rules never mind follows them, making !asklemmy@lemmy.ml a free-for-all.
Just DM someone with an A and you are good
Some instances like Hexbear.net have general megathreads where people rant under spoiler tags like this:
!rant@lemmy.sdf.org maybe