Well posts that go like:
성인용 및 성인용 콘텐츠를 보려면 video.org에 가입하고 모든 친구를 초대하세요.
헐 이거 번역해주시면 감사하겠습니다
((Disclaimer, this is not an actual link, it's just a text I translated to Korean as an example xD
As a prideful writer, I am disheartened whenever I see misguided so-called 'writers' type up collaboration posts. Yes, producing comics can just be for the fun of it, but there are many artists that really put a lot of their heart and soul into their work and really don't deserve to deal with half the crap that is out there. I understand, many of them may just be young, inexperienced, or not so good at English. But people really need to take a hard look at themselves and their abilities out of self-respect. I'm only saying this, because most of the 'writers' don't even take the proper time to concoct a reasonably structured post and yet have a guts to request help from hard working artists.
But yea, I also don't like those purely sub-for-sub posts either. People need quality subs and a loyal fan base that appreciates their work, not an army of rocks.
As you mentioned, it would be refreshing to see more off-topic posts, or any other kind of discussions not solely related to promoting our stuff.
everytime I see 70/30 once the comic earns, it always seems so bogus to me.
like come on, if they value writing they should value art too, just not for free.
Like most people sub4sub and its varieties. I also get tired of the posts that literally don't have a point. They are either giant essays about a vague topic or are vague about what the OP is looking for in terms of feedback. I don't mind giving feedback or voicing my opinion on a subject but I like to know how to phrase my responses.
Venom starts splashing out of my pores as a natural body response when I see these threads 
Hope we will get a better moderation system to avoid them ^^
i've actually been really enjoying the character questions threads that pop up even though i don't participate in them often and i'd honestly like to see more in a similar vein that motivated folks to think about their characters personalities and what not in depth
threads that dive into worldbuilding would be really cool too. i'm not sure how one would go about making one but idk stuff that gives inspo in terms of ways you could flesh out your stories world
lore threads would be cool too. something like obscure lore from your story or lore bits you've yet to reveal but with emojis or memes or something because those are always pretty fun.
i'm not too big on art trades tho that's more a personal things but casual drawing "challenges" would be nice. something like a color prompt or a word or something just to kind of serve as a collective warm up for those who wanna hop in on it and maybe on the other side something like little writing exercises to practice stuff like dialogue or how to describe stuff and so on
i won't bother getting into thread types i'm not fond of since i think we all tend to come cloaws out at a lotta the same stuff so i'd rather give ideas or suggestions to threads i think could contribute to some more interesting or hopefully useful conversations.
I muted the Promotions category a while back 
. I still find new comics from time to time and the forum is a lot quieter (in a good way). Would recommend!!
I'm with @Legendofgenii - I always get a little bummed out reading big complaint threads about this or that genre/style.
I also enjoy the character threads that ask questions because then it's not just promote-promote-promote. Having a question or a game makes it fun! 
(I really love worldbuilding/lore... maybe I could think of thread topics eventually for that.)
I dislike the threads where it's just people trying to promote specifically their work. Like its not even a share thread but just their work. I'm sorry but no one deserves attention on their creations just for existing. Everyone here works hard and I feel it's unfair when those kind of threads clog up the feed.
It seems like a lot of posts lately are people asking for critique on their series, like they've seen the popularity of some of the review threads and want in on that. But if someone does take the time to read through through their comic and leave critique on it, they either never respond or respond suuuuper defensively. Like, you're the one who asked for the critique! What did you expect? For someone to hug you and kiss your forehead and tell you that you aren't doing a single thing wrong and it's not your fault at all that your comic isn't doing well? It's not because of your bad coloring or your illegible dialogue or your unnecessarily purple prologue, no way!
It feels like "please critique my comic and tell me what I'm doing wrong" threads either want validation and tell them they're flawless victims of an unfair system, or they want one easy trick to fix all their problems and make their comic magically popular enough to make them a ton of money. Instead, they're told that they have a lot of things to fix that will require working and studying and practicing and probably years of artistic growth.
Welcome to the world the rest of us live in! We didn't pop out of the womb born with artistic abilities, we worked at it and studied it for our entire lives, and listened to artists better than us when they critiqued our work so we could improve.
I'm highly allergic to nearly every "writer looking for artist" threads. It's not always a thread though, the amount of times these people DM too because they see "pretty art" and suddenly want to collab with your arse. Honey, no. 
The "highly opinionated" discussion threads send my future weave flying too. Like baby, you could spend that time creating but here you are starting discussion after discussion like...you got nowhere else you gotta be? Or do? On OTHER social apps? In life???? 
On that same note, send me into the sun if I see one more complaint thread. OH LORD, do I shake my head at those. And of course, not all of them are the same but uh....actually no they're pretty much the same.
Oh God, the "looking for artist" one always kills my soul a little. It's bad enough you want to split the revenue in your favor but then you write the post with blatant spelling errors. (I let it slide if English isn't their first language but come on.)
To piggyback of review threads, the ones that die and then turn into link graveyards irritate me. I do understand that no one is obligated to do a hundred comic reviews if they don't want to, but if you make a "I'll review your comic/novel thread", don't abandon it without notice. Please, if you leave, say something or ask a mod to close it. Whenever I see a thread pop up that was started months or even years ago because people are dropping links like the op is even going to get back to them, it's just sad. I feel for those people, desperate for feedback, but also it's bothersome. Look with your eyes, people! When was the last time this person was even in the forums!? How are they going to review a comic or novel for you?!
And this even discounts the one or two times review thread is started and then not a single review is made.
Oh em gee yes! Don't volunteer to do reviews if you aren't actually going to do them! And put a cap on link submissions if you're getting overwhelmed! There's nothing wrong with saying "I'll review the first five people who post here," and calling it there.
I agree with all of these opinions, I'll also add the "gotcha" thread pity party, where someone is asking for critique or help, but in actuality they just want to confirm how bad they think they are. When you offer simple advice that is as nice as can be, they just counter with "it's because I freakin suck and I'm never going to do this right." and it's like...I'm a fool for responding, got it.
Plenty of my pet peeves got mentioned already, but also, hidden unpaid collaboration. No, "it's paid when we get big on webtoons" isn't paid, it's revenue share, it's probably not going anywhere because you can't be honest with your artist, too.
A lot of threads got mentioned, but there's also individual posts - people who just reply to you with a promo of their comic and run, or just spam post in 10 threads at once with a link and maybe a thumbnail. You're gonna... Tell me why I should like the comic? Why did you feel that you could cash in a really shallow compliment to get me to click the link? Did you even read the OP with the rules (happens a lot with LGBT+ shares and other types of link shares)?
Every now and then one of those users shows up complaining they're not getting any engagement. You pushed away people that might've considered reading before they even clicked a link, of course it's bad.