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.
yooo this happens so often! Back in the day I tried to start some threads to put books in my own library. The only rule really was that I didn't want to read any romance and like 50% of the submissions were romance lol. No one read the freakin rules.
I misread a thread once and felt like the scum of earth when I came back later and noticed my comic didn't belong there ;_; Can't wrap my head around people thinking you're just going to accidentally fall in love with something you weren't looking for, with zero context as to why.
As a mod I'm obligated to browse through all the new threads each day I log on, though some slip through what is posted as New for me for some reason. But yes, after sub 4 sub, I can definitely say looking through the "Help me get to X!" and unpaid collabs is tiresome. 
I feel this in my soul! LOL
A while back I would leave reviews/critiques for novels that asked for them. I would type several paragraphs for the person and sometimes they wouldn't even give what I posted a like. You know, just acknowledge that I put in some effort for something you asked for, please. Even worse is when they respond to a post after yours, leaving your review further in the dust.
I now am less likely to give any feedback unless I see they take it well beforehand.
That “why you stopped reading a comic/novel” thread hurt so bad. I didn’t even read more than a few responses and I just kept feeling like every post was about my work. Threads that only have negative comments on people’s work really scare me. They’re not adding anything productive and seem more like vague-posting than anything else. Idk I struggle with imposter syndrome 90% of the time and stuff like that makes me want to lay down and never work on anything ever again.
The “looking for artist” threads only really bug me because it’s so unbalanced. Please pay your artists and do so fairly!! There’s a lot of work that goes into each panel!
I also agree that the ones that are just for promoting a single comic or novels every update are tacky. I skip right over those.
My first post on here was a discourse thread about my comic and how others would act meeting the main character/discovering his magic. I felt that introducing my story and OC would only be beneficial if it was a shared experience and I got to learn about a lot of other characters and stories with it. Looking back it does seem a bit exploitative, as the emphasis was on my work, but it was still nice to meet people and RP a little bit.
Gotten a few of those. It's not fun to be ignored or even kind of attacked for doing what is essentially a favor. I usually like and bookmark the reviews I get for future reference. Though there was one time I didn't (cuz I thought it was a poor review) but I still said thanks anyway!
Yes! It takes so much time and effort and experience to write up a good review, and it's so infuriating when the OP doesn't respond or like or anything. Even worse, if they find some flimsy excuse for every single point you brought up and brush it off casually, like you didn't just spend half an hour of your time trying to help them out.
Or almost worse, you spend all this time and effort to write up a really in-depth review, and you point out several places where they're really successful, and a few points where they could improve, and provide draw-overs or links to references they can use to improve, and their response is...
Thanks.
It makes it hard to convince myself to take the time to critique people when they ask for it if that's the appreciation that comes of it.
I've come to either actively avoid these kinds of threads of blow thru them at the speed of sound because half my stories are merely in development and i refuse to have these kinds of takes kill what little motivation i already have
like i'm all for opinions on what people like or don't but when there's much heavier emphasis on the negative rather than a balance in weighing the both the bad and the good then i'm just going to ignore it
one of the reasons i'm just looking through the door crack of this thread because the complaints about threads 99% of the time are about the same thing we always complain about. more suggestions on what to add to improve things rather than ragging on the usual suspects please 
Yes! Catch me getting no response after spending two hours on a review and you might catch me throwing something at the nearest wall.
And I know someone doesn't have to like or agree with anything I say in a review but damn if it isn't disheartening to get nothing at all.
Oof, that's legit, and I'm sorry I didn't think more about the negative impact before participating in that thread. Personally I found some of the points brought up to be useful, as it made me rethink some things I'd been considering for my story, and I find it easier to adjust my plans preemptively than to change a plot point that's already in my story, but yeah... I also suffer from imposter syndrome, and I can definitely see how that kind of thread would not help.
I think most of the actual post types have been named by now, so I'll mention a type of response that I've come to dread...
I avoid sub for sub threads, and often will specifically mention that I don't do sub for sub when I participate in other promotion threads, so WHY do people still respond like, "I subbed to your story, support me too!". I recently stopped posting my "thanks for subscribing" graphic to people's walls because somebody responded to it asking that I sub to their comic that I'm not interested in (and guess what? They don't ever read my novel!!).
