That way I can post like "/me WHACKS you with a comically large hammer" and then have a little thing on my post that let's you know you shouldn't read it if you're 6

I'm like half serious with this, I think a ranked rating system is better than "adult/not-adult", and I wish it was used in more places online (not just cohost). Newgrounds has been using that system for years, and even websites like e621 have "safe/questionable/explicit" ratings, but it's largely absent from the internet as a whole.
I just think it would be a lot easier for everyone if they didn't have to worry about a suggestive joke being "adult content" when they could instead tag it as mature or teen (depending on exactly how suggestive it is). Then again maybe that would just start arguments about whether something was properly rated