h3h3productions / Ethan and Hila - The first one: in which some guy (Ethan) mocks YouTube videos. The second one: the alternate channel, which also has Hila who is usually behind the camera for the former. YouTube goofs and gaffes. Not exactly highbrow and sometimes offensive but funny. They seem to be softening up lately, I think they are starting to get disillusioned with the number of similar channels who take it all way way too far. This definitely fulfils your first criterion, OP. There is a community and a subreddit and lots of in-jokes. Probably overlaps a bit with 4chan users as well, so beware.
WheezyWaiter - Vlog. Craig changed his style (very Casey Neistat-esque now, although I'm not really familiar with his work) although I wasn't actually watching it before this. I like that it's quite candid, he talks about how he is trying to achieve his goals, maintain good habits, etc. It feels pretty real. I like how his morning routine grounds the video in reality and that he messes about with film techniques but the show mostly consists of... a regular guy going about his day and work.
Brian Limond - AKA Limmy. Glaswegian comedian. He had a TV show on the BBC and since then seems to have gone back to making silly vines and live-streaming his techno sessions.
Community channel - Vlog. Sketches about everyday awkwardness, comment replies, self-deprecation. There's something really chilled out about these. I may have binge watched them. They're updated in theory every week, usually every few weeks. But there are loads because it's been going since 2006.
That Japanese Man Yuta - Vox populi in Japan. I like how through asking random people on the street it manages to shed light on what Japanese society is like, without claiming to be an authority on it.
Channel Criswell / Now You See It / Every Frame a Painting / Nerdwriter1 - I'm a sucker for those smoothly-edited film analysis montage videos, although the Nerdwriter does videos on other topics (such as politics, some opinion pieces and other kinds of art analysis) and previously had more of a vlog format (which was also good). Does anyone know of any other good film analysis videos?
Don't Hug Me I'm Scared - Less a regularly-updted YouTube channel and more a series of animations that happens to be on YouTube. They're quite disturbing. I know the whole stop-motion/Sesame Street format has been subverted more times than the members of Wu Tang Clan have fingers, but this one is good.
Easy German - German-language vox pop with English subtitles, for people learning German. Updated every week. The Easy Languages channel has many more videos in other languages. I learned German in school to a sort of clunky intermediate level, so having something that is both relaxing/interesting to watch and refreshes my German ability is the best thing ever. If anyone knows any other good German-language channels or videos, I'd love to know about them!!
bill wurtz - Musician. He did that history of japan video, his other posts are mostly smooth jazz vines and a few ridiculously vapid songs, e.g. "i'm crazy/it's raining".
Cooking With Dog - A dog called Francis narrates recipes in a thick Japanese accent. Very relaxing and interesting, they have a good variety of dishes!
Kermode & Mayo - The channel for the BBC Radio 4 film review program. Loads of in-jokes, this has a bit of a cult following in the UK. Simon Mayo presents/interviews guests and Mark Kermode reviews the films. Kermode rants are... quite something.
Londonist - Showing off less well-known aspects of London, with an emphasis on the transport network. I was brought up on Transport Tycoon so this really resonates with me. I really loved recognising landmarks that were mentioned on the show, while I was living in London. Regardless of where you live, it's a good idea to learn a bit about its history - being able to see the thing you have learned about makes it so much more real and satisfying.
Novara Media - The self proclaimed "BuzzFeed of the Left". They also have articles (listicles and long-form, both worth reading) and a weekly podcast on their website which airs on Resonance 104.4 FM every Friday at 1pm if you're in Central London. They cover international, anti-imperialist, gender, LGBT, economic, human rights issues. The online videos are a pretty new addition and I think that they are still a bit rough around the edges, but it's great that someone knows what the British left needs - to educate people on how to understand and deal with the issues that plague their lives and those of people around the world. Sometimes they trip up on discourse-speak but they seem to be improving. The Artist Taxi Driver is also pretty good at this, but he did model himself on opinionated taxi drivers so he is... kinda grating.
Frank JavCee - he posts videos sarcastically (but truthfully) showing how to produce electronic music and in doing so breaks the various ephemeral microgenres of the right now into their constituent parts. He's a damn good producer and funny. He mocks the styles of music, but in a way that indicates a love and interest for the content, which is definitely refreshing.
oh god i've written a lot